In no particular order:
The last scenes of Casablanca...plus pretty much the whole movie.
"You're all clear, kid!" From Star Wars Ep. 4....first and only time I ever yee-hawed in a movie.
The President's speech in "Independence Day".
Spock's death in Star Trek II. Cliche now but devastating when we didn't know if he was ever coming back.
The Ride of the Rohirrim in Return of the King, from Theoden's speech to when Eowyn pwns the Witch King.
For good old fashioned cheese value: the multi-monster mash up in "Destroy All Monsters"
http://www.youtube.com/watch?v=V3HuTZoCZt4&feature=relatedA bunch more but this is what I can come up with on low sleep.