Doom 3 Hints:
Martian Buddy Cabinet:
Before entering into the Alpha Labs, you will come across a locked cabinet called "FREE STUFF" by martianbuddies. You might be thinking maybe somewhere later in the game you will find a pda with the codes in it but you won't. 
The code to the cabinet is 0508. When you hit "0" the cabinet will sort of beep in error but don't worry, complete it. Once you have keyed in the codes, the cabinet will open up and you will find some ammunition, armor and a chaingun.

Doom 3 Cheats:
Bring the console up with [control] + [alt] + [~] and type the following codes in to blow the monsters back to hell:) 


aviDemo = Saves a demo of your playing to an AVI movie file 
benchmark = Game Benchmark 
doomhell = Skip all levels to last 
freeze = Freeze all on screen 
gfxinfo = Graphicscard infomation 
god = God mode 
noclip = No Clip 
notarget = Invisibility to most enemies 
com_drawfps 1 = Show FPS 
give all = Full load of weapons and ammo 
give doom95 = Load the '95 version of Doom 
give keys = Acquire all the keys you'll ever need 
give weapon_machinegun = Machinegun 
give weapon_shotgun = Shotgun 
give weapon_plasmagun = Plasmagun 
give weapon_bfg = BFG 
give weapon_chainsaw = Chainsaw 
give weapon_rocketlauncher = Rocket Launcher 
status = Your game status 
quit = Quid aka Exit 

Below is the rest of the codes. At the moment we don't have time to find 
out what they're all good for. Play around with them yourselves!! 

_use 
_moveRight 
_moveLeft 
_moveDown 
_forward 
_back 
_right 
_left 
_lookDown 
_lookUp 
_attack 
_moveUp 
_speed 
_strafe 
_button7 
_button6 
_button5 
_button4 
_button3 
_button2 
_button1 
_button0 
aasStats 
addarrow 
addline 
blinkline 
bindlist 
bind 
centerview 
compressDemo 
connect 
clearlights 
conDump 
clear 
cvar_restart 
cvarlist 
combineCubeImages 
crash 
collisionModelInfo 
dirtyfeet 
dir 
demoShot 
disconnect 
dmap 
echo 
envshot 
exec 
exportmodels 
editSounds 
editLight 
editor 
error 
fillrate 
flashlight 
focusSoundsEditor 
give 
game_memory 
in_restart 
kill 
killRagdolls 
killMoveables 
killMonsters 
keepTestModel 
listModels 
listSkins 
listMaterials 
listImages 
listModes 
listLightDefs 
listEntityDefs 
listMonsters 
listEntities 
listThreads 
listSounds 
listAnims 
listCollisionModels 
listlines 
listVertexCache 
map 
modulateLights 
noclip 
notarget 
nextanim 
overlayGUI 
path 
poplight 
parsewait 
printShader 
printMode 
playDemo 
playCmdDemo 
playerModel 
prevanim 
reload 
reloadSounds 
reloadSoundShaders 
reloadFx 
reloadanims 
reexportmodels 
removeline 
runReach 
runAAS 
recordCmdDemo 
recordDemo 
recordCmdDemo 
recordDemo 
renderbumpFlat 
renderbump 
roq 
reloadGuis 
reset 
regenerateWorld 
reloadImages 
reloadShaders 
reloadModels 
script 
reloadEntityDefs 
s_musictrack 
s_cacheInvalidate 
s_cacheInfo 
s_restart 
seta 
set 
spawn 
setviewpos 
setStepGamma 
setu 
sets 
sizeDown 
sizeUp 
screenshot 
spawnServer 
stopRecording 
say 
testTrace 
testImage 
testShader 
testBump 
testLight 
touchFx 
touchGui 
touchFile 
toggle 
testSIMD 
touchMaterial 
testFx 
touchSound 
listSoundShaders 
touchParticle 
testDamage 
testblend 
testanim 
testParticle 
testModel 
testWipe 
testGUI 
timeDemo 
testmap 
touchSkin 
touchModel 
unbind 
unbindall 
vid_restart 
vstr 
writeConfig 
writePrecache 
weapon 
weapnext 
where 
weapprev 
weaponSplat 
==========================================================

If you feel you don't wanna waste your time playing the easier difficulties to unlock nightmare difficulty you can
change the line

seta g_nightmare "0"
to
seta g_nightmare "1"

in doomconfig.cfg
--------------------------------------------------------------------------------------------------------------------------------------------------
open console
timedemo demo1.demo

this will do a benchmark
--------------------------------------------------------------------------------------------------------------------------------------------------
You can brighten the game up by typing 
"r_gamma X" in the console, where the X is a # between 0 and whatever
--------------------------------------------------------------------------------------------------------------------------------------------------
How to fix the game being too dark:

r_gamma 3 <- the highest it'll go. 3 = max.
r_brightness 0 <- yes, zero.
--------------------------------------------------------------------------------------------------------------------------------------------------
seta g_showPlayerShadow "0" - player shadows off

seta g_showPlayerShadow "1" - player shadows on

makes the game more realistic
--------------------------------------------------------------------------------------------------------------------------------------------------

Third person:
bind "p" "toggle pm_thirdperson"
--------------------------------------------------------------------------------------------------------------------------------------------------
Testsmaps: 

map testmaps/testmaps_lotsaimps.map
map testmaps/test_box.map
map testmaps/test_boxstack.map

If you cant get them to work extract the files from pak000.pk4
--------------------------------------------------------------------------------------------------------------------------------------------------
You can turn on a sound level meter! 
It shows the volume bars of the 6 different channels.

s_showLevelMeter 1
--------------------------------------------------------------------------------------------------------------------------------------------------
If you find the sound is clipping a lot, or if you 
like to keep the gain a bit lower to get a cleaner signal, 
you can adjust that too.

s_volume_dB x (default x=0; -x=lower; x=higher)
--------------------------------------------------------------------------------------------------------------------------------------------------

g_showProjectilePct 1 will add a hit percentage reading to your HUD.

-----------------------------------------------------------
CONSOLE COMMANDS SUMMARY:

aasStats shows AAS stats
addarrow adds a debug arrow
addChatLine internal use - core to game chat lines
addline adds a debug line
aviCmdDemo writes AVIs for a command demo
aviDemo writes AVIs for a demo
aviGame writes AVIs for the current game
benchmark benchmark
bind binds a command to a key
bindRagdoll binds ragdoll at the current drag position
bindunbindtwo binds a key but unbinds it first if there are more than two binds
blinkline blinks a debug line
centerview centers the view
checkNewVersion check if a new version of the game is available
clear clears the console
clearLights clears all lights
clientDropWeapon drop current weapon
clientMessageMode ingame gui message mode
clientVoiceChat voice chats: clientVoiceChat 
clientVoiceChatTeam team voice chats: clientVoiceChat 
closeViewNotes close the view showing any notes for this map
collisionModelInfo shows collision model info
combineCubeImages combines six images for roq compression
compressDemo compresses a demo file
conDump dumps the console text to a file
connect connects to a server
crash causes a crash
cvar_restart restart the cvar system
damage apply damage to an entity
debugger launches the Script Debugger
deleteSelected deletes selected entity
demoShot writes a screenshot for a demo
devmap loads a map in developer mode
dir lists a folder
dirtree lists a folder with subfolders
disasmScript disassembles script
disconnect disconnects from a game
dmap compiles a map
echo prints text
editAFs launches the in-game Articulated Figure Editor
editDecls launches the in-game Declaration Editor
editGUIs launches the GUI Editor
editLights launches the in-game Light Editor
editor launches the level editor Radiant
editParticles launches the in-game Particle Editor
editPDAs launches the in-game PDA Editor
editScripts launches the in-game Script Editor
editSounds launches the in-game Sound Editor
envshot takes an environment shot
error causes an error
exec executes a config file
execMachineSpec execs the appropriate config files and sets cvars based on com_machineSpec
exit exits the game
exitCmdDemo exits a command demo
exportmodels exports models
finishBuild finishes the build process
freeze freezes the game for a number of seconds
game_memory displays game class info
gameError causes a game error
gameKick same as kick, but recognizes player names
getviewpos prints the current view position
gfxInfo show graphics info
give gives one or more items
god enables god mode
heartbeat send a heartbeat to the the master servers
help shows help
hitch hitches the game
in_restart restarts the input system
keepTestModel keeps the last test model in the game
kick kick a client by connection number
kill kills the player
killMonsters removes all monsters
killMoveables removes all moveables
killRagdolls removes all ragdolls
LANScan scans LAN for servers
listActiveEntities lists active game entities
listAF lists articulated figures
listAnims lists all animations
listAudios lists Audios
listBinds lists key bindings
listClasses lists game classes
listCmds lists commands
listCollisionModels lists collision models
listCvars lists cvars
listDecls lists all decls
listDictKeys lists all keys used by dictionaries
listDictValues lists all values used by dictionaries
listEmails lists Emails
listEntities lists game entities
listEntityDefs lists entity defs
listFX lists FX systems
listGameCmds lists game commands
listGuis lists guis
listHuffmanFrequencies lists decl text character frequencies
listImages lists images
listLines lists all debug lines
listMaterials lists materials
listModelDefs lists model defs
listModels lists all models
listModes lists all video modes
listMonsters lists monsters
listParticles lists particle systems
listPDAs lists PDAs
listRenderEntityDefs lists the entity defs
listRendererCmds lists renderer commands
listRenderLightDefs lists the light defs
listServers lists scanned servers
listSkins lists skins
listSoundCmds lists sound commands
listSoundDecoders list active sound decoders
listSounds lists all sounds
listSoundShaders lists sound shaders
listSpawnArgs list the spawn args of an entity
listSystemCmds lists system commands
listTables lists tables
listThreads lists script threads
listToolCmds lists tool commands
listTypeInfo list type info
listVertexCache lists vertex cache
listVideos lists Videos
loadGame loads a game
localizeGuis localize guis
localizeMaps localize maps
makeAmbientMap makes an ambient map
MakeMegaTexture processes giant images
map loads a map
memoryDump creates a memory dump
memoryDumpCompressed creates a compressed memory dump
modulateLights modifies shader parms on all lights
nextAnim shows next animation on test model
nextFrame shows next animation frame on test model
nextGUI teleport the player to the next func_static with a gui
nextMap loads the next map on the server
noclip disables collision detection for the player
notarget disables the player as a target
parse prints tokenized string
path lists search paths
playCmdDemo plays back a command demo
playDemo plays back a demo
playerModel sets the given model on the player
popLight removes the last created light
prevAnim shows previous animation on test model
prevFrame shows previous animation frame on test model
printAF prints an articulated figure
printAudio prints an Video
printEmail prints an Email
printEntityDef prints an entity def
printFX prints an FX system
printMaterial prints a material
printModel prints model info
printModelDefs prints a model def
printParticle prints a particle system
printPDA prints an PDA
printSkin prints a skin
printSoundShader prints a sound shader
printTable prints a table
printVideo prints a Audio
promptKey prompt and sets the CD Key
quit quits the game
rcon sends remote console command to server
reconnect reconnect to the last server we tried to connect to
recordDemo records a demo
recordViewNotes record the current view position with notes
reexportmodels reexports models
regenerateWorld regenerates all interactions
reloadanims reloads animations
reloadARBprograms reloads ARB programs
reloadCgPrograms reloads CG programs
reloadDecls reloads decls
reloadEngine reloads the engine down to including the file system
reloadGuis reloads guis
reloadImages reloads images
reloadLanguage reload language dict
reloadModels reloads models
reloadScript reloads scripts
reloadSounds reloads all sounds
reloadSurface reloads the decl and images for selected surface
remove removes an entity
removeline removes a debug line
renderbump renders a bump map
renderbumpFlat renders a flat bump map
reportImageDuplication checks all referenced images for duplications
reportSurfaceAreas lists all used materials sorted by surface area
rescanSI internal - rescan serverinfo cvars and tell game
reset resets a cvar
roq encodes a roq file
runAAS compiles an AAS file for a map
runAASDir compiles AAS files for all maps in a folder
runReach calculates reachability for an AAS file
s_restart restarts the sound system
saveGame saves a game
saveLights saves all lights to the .map file
saveMoveables save all moveables to the .map file
saveParticles saves all lights to the .map file
saveRagdolls save all ragdoll poses to the .map file
saveSelected saves the selected entity to the .map file
say text chat
sayTeam team text chat
screenshot takes a screenshot
script executes a line of script
serverForceReady force all players ready
serverInfo shows server info
serverMapRestart restart the current game
serverNextMap change to the next map
set sets a cvar
seta sets a cvar and flags it as archive
setMachineSpec detects system capabilities and sets com_machineSpec to appropriate value
sets sets a cvar and flags it as server info
sett sets a cvar and flags it as tool
setu sets a cvar and flags it as user info
setviewpos sets the current view position
showDictMemory shows memory used by dictionaries
showInteractionMemory shows memory used by interactions
showStringMemory shows memory used by strings
showTriSurfMemory shows memory used by triangle surfaces
showViewNotes show any view notes for the current map, successive calls will cycle to the next note
sizeDown makes the rendered view smaller
sizeUp makes the rendered view larger
spawn spawns a game entity
spawnServer spawns a server
startBuild prepares to make a build
stopRecording stops demo recording
takeViewNotes take notes about the current map from the current view
takeViewNotes2 extended take view notes
teleport teleports the player to an entity location
testAnim tests an animation
testBlend tests animation blending
testBoneFx tests an FX system bound to a joint
testDamage tests a damage def
testDeath tests death
testFx tests an FX system
testGUI tests a gui
testImage displays the given image centered on screen
testLight tests a light
testmap tests a map
testModel tests a model
testParticleStopTime tests particle stop time on a test model
testPointLight tests a point light
testSave writes out a test savegame
testSaveGame test a save game for a level
testShaderParm sets a shaderParm on an existing testModel
testSIMD test SIMD code
testSkin tests a skin on an existing testModel
testSound tests a sound
testVideo displays the given cinematic
timeCmdDemo times a command demo
timeDemo times a demo
timeDemoQuit times a demo and quits
toggle toggles a cvar
touch touches a decl
touchFile touches a file
touchFileList touches a list of files
touchGui touches a gui
touchModel touches a model
trigger triggers an entity
unbind unbinds any command from a key
unbindall unbinds any commands from all keys
unbindRagdoll unbinds the selected ragdoll
updateUI internal - cause a sync down of game-modified userinfo
vid_restart restarts renderSystem
vstr inserts the current value of a cvar as command text
wait delays remaining buffered commands one or more frames
weaponSplat projects a blood splat on the player weapon
where prints the current view position
writeCmdDemo writes a command demo
writeConfig writes a config file
writeGameState write game state
writePrecache writes precache commands