Jazz Jackrabbit

Pause the game with [P], then press [Backspace],
then enter the code.  Registered version need
'DD' in front of the codes (eg: 'ddbad')

tim     Displays 'Awesome'
mark    Suicide and return to start
arjan   Displays 'Hahaha'
apogee  Try it !
ken     Quit to Dos
hocus   Displays 'Abracadarbra', teleports
doom    Makes everything harder to kill
greetz  Displays some info
check   Display some numbers (coordinates?)
lamer   skips current level
sable   Turn red and run faster
gunhed  full inventory !
bouf    Temporarly invicible  (also boud)
bad     Gives you the bird
cstrike Gives you the airboard
hooker  Yellow flash, prepares bonus level

Or press [F10]+[F11]+[F12] at the level select.