There's Something About Mary
Anchorman
Bruce Almighty
Monty Python and the Holy Grail
Donnie Darko (I know, strange but I find the funny parts of this movie absolutely hilarious)
Pineapple Express
I see Tropic Thunder being mentioned a lot, but for some reason I find this movie really, overall, poorly excecuted. Ben Stiller is unfunny and terrible as usual, Jack Black is just there, only Downey Jr. does a good job.
However, I did find the opening scene of Tropic Thunder (the opening warzone scene) side-splittingly hysterical. it set the bar waaaay too high for the rest of the movie and the rest was just disappointing.