For just showing off the system LFE capabilities, I throw in the Tri-pod scene. It's pretty impressive and I can kick folks out of the room in about ten minutes.

As Robb mentioned, LOTRs is a great movie (all of them) for continued sound effects.

Another good one is the Harry Potter movies. The last one in particular. The second one had my girlfriend swatting the air behind her head when the keys were flying around (forgot what part of the movie that was, but it sure was funny watching her try to swat nothing but air).