Versus mode:
Successfully complete the game on any difficulty setting to unlock versus mode with five frames and most stages. Successfully complete the game on any difficulty setting twice to unlock the remaining two frames and stages.

To unlock Versus Mode the easy way, press CIRCLE, X, RIGHT, LEFT, RIGHT, LEFT, DOWN, DOWN, UP, UP at the title screen. If you entered it correctly, you'll hear a sound and "Versus" will appear at the main menu.

Different ending music:
Complete the game on each difficulty with an "A" rank on all five rescue missions.

Unlock 2 extra stages: [Submitted by:Smurf]
Complete the game on any difficulty level with a rank "D" or above to enable the versus option on the main menu.
Complete the game a second time to unlock the remaining two orbital frames and two battle levels in versus mode.

Full health and ammunition: [Submitted by:Luggs]
Pause the game and press L1(2), L2(2), L1, R1, L1, R1, R2, R1. Note: Each time this code is used your level will go down by one.

Invincibility: [Submitted by:Gez]
At the starting screen enter: L1x5 R1x3 start and select.
please note you do not have to enter these cheats quickly so take your time!!!