R-Types

Unlock the "Stage Select" option:
Highlight either the "R-Type" or "R-Type II" options at the title screen.
Quickly press L2(10 times), R2(10 times). Begin game play and press Start.

Bonus credits:
While you are at the title screen, repeatedly press Select to get up
to 99 credits. You can also do this at the countdown on the game over
screen to continue. This trick works in all R-type games.

Speed select:
Press Start to pause game play, then hold L2 and press Right, Up, Right,
Up, Down, Left, Down, Left. - Then, press O to increase or
X to decrease the speed. This trick works in R-Type and R-Type II.

Invincibility cheat:
Press Start to pause game play, then hold L2 and press Right(2 times),
Left, Right, Left(2 times), Right, Left, R2, Up(2 times), Down(2 times),
Up, Down, Up, Down, R2. If you entered correctly, you will hear a sound.
This trick works in R-Type and R-Type II.

All weapons code:
Press Start to pause game play, then hold L2 and press Right, Up, Left,
Right, Down, Left, Up, Right followed by one of the following buttons
for various weapons: Triangle, Square, X, Circle, or R1.
This trick works in R-Type and R-Type II.