Mini-Games: Go to the options menu and go to the text credits. When you find the text for the minigames, press A. If done right, the A in Games will look like the A on the controller. 

Unlock Turbo Cheat: Earn 275 championship points
Unlock Saturate Cheat: Earn 300 championship points
Unlock Edgy Cheat: Earn 325 championship points
Unlock Pop Video Cheat: Earn 375 championship points 

Unlock Season Highlights: Finish first in any track
Unlock Sheridan Track: Complete all the challenges in championship
Floating Bike Mode: Edit logo on your custom bike to read: kingpin
Unlock Legend Difficulty: Win the championship on champion difficulty 

Unlock Carlos Chera: Get an overall total of 100,000 points in stunt mode 
Unlock Alex Barros: Get an overall total of 250,000 points in stunt mode 
Unlock Max Biaggi: Get an overall total of 500,000 points in stunt mode 
Unlock Tohru Ukawa: Get an overall total of 750,000 points in stunt mode 
Unlock Valentino Rossi: Earn an overall total of 1000000 points in stunt mode