Here's some favorites of mine. I'm a big sci-fi fan, which really shows in my list.
No way I could put them in order of greatest to least greatest as that changes with my mood, heck even trying to narrow down this list is hard enough as it is without putting them in order, and I won't be able to keep it to just 10, sorry, I've watched way to many movies in my time:
-Anchorman
-Back to the Future Trilogy
-Batman (1989)
-Batman Begins
-Conan the Barbarian & The Destroyer
-The Crow
-Dawn of the Dead (Original & Remake)
-Day of the Dead (Original ONLY, the remake (in name only) was TERRIBLE)
-Demolition Man
-Detroit Rock City
-First Blood
-Ghostbusters 1 & 2
-Grandma's Boy
-Half-Baked
-Hook
-Independence Day
-Iron Man
-League of Extraordinary Gentlemen
-The Lord of the Rings Trilogy
-The Lost Boys
-The Monster Squad
-A Nightmare on Elm Street series (Awful remake not included)
-Predator 1 & 2
-Robocop
-Shaun of the Dead
-Sin City
-Starship Troopers
-Star Trek Movies (1, 2, 3, Generations, and First Contact in particular)
-Terminator 1 & 2
-Universal Soldier
-X2: X-Men United