Considering the LOTR Trilogy is an 11hr movie, I thought this would be a cool debate. Feel free to throw in your favorite overall scene, even if it is not an "action" sequence.
Here's my vote:
1. The Balrog battle between Gandalf and the Balrog in FOTR.
2. Shelob vs Sam, in ROTK.
3. The Witch King vs Eowyn in ROTK.
Overall, an amazing trilogy...I can't wait for The Hobbit, and I can't wait for the extended DVD in August.