Press P to pause the game and type in these codes.

CodeEffect
boosterFull energy
luehmannInvincible
just cut to the endSee ending video
go anywhere Level select
fruitGo to Anything But Tangerines  
dublinGo to Puppy Love 
hoffmanGo to Flyin Kin 
abrown Go to Cow Abduction 
shiny shines Go to Inflated Head 
                                        

Note that these codes only work for the US version.      

Thanks to Revolution readers John Case III and Duderonamee!