Tucker and Dale Vs. Evil
Chosen by me for my Whedon actors in horror comedies theme week
A clever inversion of the usual slasher in the woods films like Friday the 13th and hillbilly gone bad movies like Deliverance this can't quite sustain it's running time (it repeats it central gag - that the college kids are incredibly accident prone - a touch too much) but is funny and often quite clever.
Tudyk and Labine are in fine form, dumb but with enough of a sympathetic touch (their exasperation at a bunch of kids who seem hellbent on a suicide pact is delightful) to stop them being just hick cliches.