Like many of the rest of you:
Blazing Saddles/Mel Brooks
Airplane!
Dumb and Dumber
The Hangover
Any Monty Python
The Big Lebowski
Kevin Smith movies
Also:
Bad Santa. A personal favorite, and annual Christmas watch for me and my girlfriend.
Me, Myself, and Irene
Billy Madison/Waterboy
Jackass Movies
Pink Panther