Tony Hawk's Pro Skater 3

Enter the options menu, then choose the "Cheats" selection. 
Enter "magicmissile" as a code to unlock all mode options.
Enter "backdoor" as a code to unlock all cheat options.
Enter "roadtrip" as a code to unlock all levels.
Enter "yohomies" as a code to unlock all characters.
Enter "givemesomewood" as a code to unlock all decks for the current skater.
Enter "Peepshow" as a code to unlock all movies under the options menu.
Enter "PUMPMEUP" as a code to unlock full stats for your character. 

If cheats entered correctly, you will hear the sound of money being collected. 

Cheat Mode
Play as usual then pause the game, hold fast spin left, then press up, 
grind without releasing the fast spin left button, then go to the menu, 
and select end run.