Red beam mode:
Press Right, Up, Left, Circle, Up, Circle, Circle.

Ten additional missiles:
Press X, Circle, R1, Right, Triangle, X, Triangle.

Ten additional grenades:
Press R1, X, R1, Right, Square, Right, Square.

Full health:
Press R1, Triangle, L1, Left, Triangle, Circle, X.

Level select:
Press Up, Left, Down, R2, Right, Square, X.

Unlimited lives:
Begin game play and reach the Craterscape level. Take the extra life located behind the pillar on the bridge at the start of the level. After the total number of lives has increased, press Start, Select, and use the "Quit" option. Select "Yes" to confirm to return to the title screen. Select the "Start" and "Continue current game" options to restart at the Craterscape level. Collect the extra life again from the pillar and repeat this process to accumulate as many lives as desired.