Well, I cry at a lot of movies. Hell, I had to hold back the tears while watching Lemony Snicket on a plane - and I had even seen it before. These really get me going, though:
Empire of the Sun
Return of the King
Moulin Rouge
F9/11 (the part with the mother reading the letter from her son)
Shaun of the Dead (no, not just tears of laughter - I break down at least 3 times watching this one)
That's all I can think of, at the moment.