I am shocked and appalled that The Ice Pirates is not in any of these lists!

Alright, seriously, here's my list:
1) Star Wars IV: A New Hope
2) Star Trek II: The Wrath of Khan
3) Predator
4) Terminator 2
5) Back to the Future
Honorable mentions: Aliens, A Clockwork Orange, and Pitch Black.
I also recognize 2001 probably deserves to be on a more objective top 5 list, but I'm assuming we're talking about personal top 5s here.