Type in these codes at any menu:

BUBBLES - Cheat mode on
IAMZEUS - God mode toggle
FULLMONTY - Level select toggle
LUMBERJACK - Missle toggle on. Hit Mug quick key once for normal, twice for spiraling Mug, three times for bouncy Mug.
Hit Solaris quick key once for normal, twice for homing plasma, three times for powerful blue homing plasma.
JIMBEAM - Beam toggle on. Hit laser quick key onece for normal laser, twice for electro-beam, three times for superbeam.