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

Code                    Effect
booster                 Full energy
luehmann                Invincible
just cut to the end     See ending video
go anywhere             Level select
fruit                   Go to Anything But Tangerines    
dublin                  Go to Puppy Love         
hoffman                 Go to Flyin Kin  
abrown                  Go to Cow Abduction     
shiny shines            Go to Inflated Head 
                                        

Note that these codes only work for the US version.