Not in any order, and this is just off the top of my head
- Gran Torino
- Billy Madison
- The Naked Gun
- Shawshank Redemption
- Inception/Shutter Island (tie)
Other great movies: Inglourious Basterds, Aliens, No Country For Old Men, Batman Begins, American History X, Saving Private Ryan, First Blood, etc.
Horrible movies that are way overrated: The Godfather, Scarface, Monty Python and the Holy Grail, Casino Royale/Quantum of Solace, etc.