Double Laser:
Up, C-Up, Up, C-Up

Triple Laser:
Right, Right, C-Left, C-Down

Four-way fire:
Down, Down, Up, C-Right

Shield:
Down, Left, C-Left, C-Right

Flame Thrower:
Down, Right, Down, Right, C-Right

Speed Up:
Left, Left, Right, Right, C-Up

Radiation Spray:
Up, Down, C-Right, C-Left

Enter the next three codes quickly at the Setup menu:
50 Lives:
Press Up, Up, Down, Down, Left, Right, Left, Right, C-Left, C-Right, C-Left, C-Right.

Level select:
Press Down, Up, C-Left, Down

Game boy mode:
Up, Down, Right, C-Left, Down, Up, Left, C-Right, Up, Down

Thanks to Revolution readers ChrisFarley#1fan and Computer Spawn!