Cheat mode

Hold L1+R1+R2 and press Select to enable cheat mode. If you entered the code correctly, "Cheats Enabled" will appear at the top of the screen. Then, one of the following codes may now be enabled:

God mode

Hold L1+R1+R2 and press Up, Down, Left, Right.

Invulnerable

Hold L1+R1 and press Up, Down, Left, Right.

Infinite weapons

Hold L1+R1 and press Up, Down, Up, R2.

Powered-up weapons

Hold L1+R1+R2+X and press Down.

Hornet nest stingers

Select stingers, then press L1+L2+R1+Triangle+Left.

Play as Big Daddy

Enter Triangle, Square, R2, X, Triangle, R2 as a password. Then select "Challenge" mode and choose the "Nuke York" level to enable Big Daddy on the vehicle selection screen.
Submitted by Nintendosnut

Play as Alien saucer

Enter R1, Square, X, Square, L2, Circle as a password. 
Submitted by Nintendosnut

Play as Goliath

Enter Triangle, L1, R1, X, L2, L2 as a password.
Submitted by Nintendosnut

Play as Nightshade

Enter R1, R2, L1, L1, X, Circle as a Password.
Submitted by Nintendosnut

Play as Helicopter

Enter L1, Triangle, R2, Triangle, Triangle, R1 as a password.
Submitted by Nintendosnut

Funtopia level

Enter X, Circle, L2, X, Square, L1 as a password to unlock the Funtopia level under "Challenge" mode. 
Submitted by Nintendosnut

Gulch level

Enter X, Square, Circle, L1, L2, Square as a password to unlock the Gulch level under "Challenge" mode. Alternately, enter Square, Square, Triangle, R1, L1, Circle as a password.
Submitted by Nintendosnut

Boss Battle 1

Enter Circle, R2, R1, Square, L1, R2 as a password. Note: Re-enter this code after every challenge battle. The first opponent will be a normal, random, character. Your opponent will transform into a Goliath after the battle.
Submitted by Nintendosnut

Boss Battle 2

Enter Circle, Circle, L2, L1, Triangle, Triangle as a password.
Submitted by Nintendosnut

Boss Battle with Big Daddy

Enter Square, Triangle, Circle, Circle, R2, R2 as a password. Then select "Challenge" mode and choose "Nuke York" level to battle against Big Daddy.
Submitted by Nintendosnut

Double pick-ups

Enter L1, L2, Circle, L1, R1, Square as a password.
Submitted by Nintendosnut

Increased armor

Enter R1, Triangle, R1, Triangle, L1, Square as a password.
Submitted by Nintendosnut

Infinite turbos

Enter Square, X, Circle, Triangle, R1, R2 as a password. Note: The special bar will still decrease, but turbos will still be available after it runs out.
Submitted by Nintendosnut

Infinite jump

Enter Circle, Square, R2, X, Triangle, R2 as a password.
Submitted by Nintendosnut

View Duke Nukem: Time To Kill FMV sequence

Enter Square, Square, Circle, Circle, Triangle, Triangle as a password.
Submitted by Nintendosnut

Alternate views

While playing a game it one player mode, hold R1+Select and press Down to switch to an overhead, and helicopter view. In multi-player mode, this will alternate how the screen is split.
Submitted by Nintendosnut

Full screen view

While playing a game, hold R1+Select and press Up to remove all items from the screen.
Submitted by Nintendosnut

Combo moves

Move Code

Jump press L1+R1
Shield Hold Triangle and press 
Up, Right, Down, Left
Stun Hold Triangle and press 
Right, Left, Up 
Cash suck Hold Triangle and press 
Left, Right, Up
Rear fire Hold Triangle and press 
Right, Left, Down
Mine Hold Triangle and press 
Left, Right, Down
Up on 2 wheels to the left Hold Triangle and press Up, Down, 
Left
Up on 2 wheels to the right Hold Triangle and press Up, Down, Right