GRADIUS

Full weapons:
Pause the game, and push Up, Up, Down, Down, Left, Right, Left,
Right, B, A, Start. This will give you missiles, options and
shield, but you can only it once per game.

Continue mode:
As soon as your last ship is destroyed , press Down, Up, B, A,
B, A, B, A, B, A on controler one. You'll need to be on stage 
two or higher, and you'll also have to enter the code quickly.


Power Up:
Press START to pause the game, then key in Up, Up, Down, Down,Left, Right, Left, Right, B, A START to be powered up.. 
you can only do this once per level.