1. "Let's face it; this isn't the worst thing you've caught me doing." -- From Iron Man, ID'd first by anton_p_nym
2. "Did you leave anything for us?" "Just bodies." -- From Commando, ID'd first by laptop_mechanic
3. "I can kill you anytime, Captain. Anytime."
4. "Ohhhh, that's not riiiight."-- From Galaxy Quest, ID'd first by k_kinnison
5. "It doesn't matter if racing ever changes. What matters is if we let racing change us." -- From Speed Racer, ID'd first by shana
6. "I have been DENIED... critical, need-to-know information!" -- From Tremors 2, ALMOST identified by a couple people, ID'd first by hallerlake
7. "I say we take off and nuke the site from orbit. It's the only way to be SURE." -- From Aliens, ID'd first by janetmiles
8. "You have freed me, traveller; now go free yourself." -- From The Forbidden Kingdom, ID'd first in a team effort. paulbearman recognized the actor (Jet Li) and the character (The Monkey King) and thus knew which movie, but shana was the one to actually recall the title.
9. "What an incredible smell you've discovered!" -- From Star Wars (and no, NOT "A New Hope"), ID'd first by janetmiles
10. "No, Mr. Bond; I expect you to die." -- From Goldfinger, ID'd first by rdmasters
11. "This hotel thinks of everything; they have even provided an assassin with room service."
12. "If you were waiting for the opportune moment... that was it." -- From Pirates of the Caribbean: Curse of the Black Pearl, ID'd first by k_kinnison and by nuranar; they apparently posted simultaneously but Kinnison is, of course, before Nuranar in the alphabet.
13. "NOT without incident." -- From the impossibly, ludicrously brilliant Equilibrium, ID'd first by randallsquared
14. "I ain't got time to bleed." -- From Predator, ID'd first by anton_p_nym
15. "T-Bolt, your parking lot is ready, sir." -- From the 2003 Ang Lee Hulk, ID'd first by ross_teneyck
16. "No matter how many times you save the world, it always manages to get back in jeopardy again!" -- From The Incredibles, ID'd first by anton_p_nym
17. "A man's got to know his limitations." -- From Magnum Force, in a sort of tie ID'd first by hallerlake and by gridlore; Hallerlake had correctly recognized the CHARACTER but designated the wrong movie, and then started firing randomly (ha ha!) in the general area until he hit, while Gridlore went straight to the correct movie.
18. "All that has transpired here has done so according to my design." -- the signature line of the Emperor from Return of the Jedi, ID'd first by ross_teneyck
19. "I noticed you stopped stuttering." "I've been giving myself shock treatments." "Up the voltage." -- From Real Genius, ID'd first by midnightlurker
20. "I'm not going to waste my time arguing with a man who's lining up to be a hot lunch." -- From Jaws, ID'd first by gridlore
Some of these are obvious, some I hope not so much.