Centipede (PSX)

Centipede cheats:

Level select
Select "Adventure" from the main menu. Press R1(2), R2, R1 when the level selection screen appears to unlock all of them.

To enter cheat mode
Press Start to pause game play in adventure mode. Press L1(2), L2, L1, then press Start to resume the game. Press Start to pause game play again. Press Right for an extra life. Note: An odd number of lives will result in invincibility. A sound will confirm correct code entry.

Extra Lives and Invincibility:
Start an adventure game and press start(to pause) during gameplay. Now press
L1, L1, L2, L1, press start to unpause, then press start to pause the game
again. Now press to the right to add an extra life, and every odd life also
makes the player invincible.

Other Sites you may consider
CheatServer.Com
Cheat Codes Club