Crash Bandicoot 3
Spyro The Dragon demo
At the main menu, press Up(2), Down(2), Left, Right, Left, Right, Square.
Hot Cold hidden level
Go to Level 14 and ride about half way through the level to find an alien crossing sign on the left hand side. Run into the sign to be transported to level 31.
Eggipus Rex hidden level
Go to Level 11 and take the yellow gem ride. Then proceed until reaching the area where the huge dinosaur chases Crash. Allow the second pterodactyl to capture Crash to reach level 32.
Instant Uka Uka (PAL version)
Press Triangle + Circle + X + Square. Note: This may only be done once per life.