Neat-o codes: 

Pause the game and slowly enter these codes: 

itsawonderful           Extra life
onandonandon            Maximum number of game continues
threemileisland         Maximum energy
iddqd                   Show developers
idkfa                   Show testers
popquizhotshot          Gives you 1000 bullets
hatman                  Stick figure mode
bloated                 Jim gets an afro
festering               Jim gets a red afro
sweaty                  Jim gets big lips
pusfilled               Jim gets antenae
malformed               Jim gets a big pair of glasses
getthecheesetosickbay   Access all levels