It seems like anything by Pixar is a good bet. I was just watching Monsters, Inc again yesterday for the first time since getting the 990/7125/LFM-2 and I was amazed. The parts where Boo laughs, causing electrical surges, were particularly fun to listen to.

One of my favorite movies is Amélie, and I was delighted at the quality of the soundtrack after watching it again with the Outlaw gear. Good mix of low and high frequencies with effective and creative use of the surrounds. Really outstanding (especially for a non-action type film), and paired with equally brilliant cinematography and a charming story with interesting characters, it's hard to beat IMHO.

One related subtopic that might make an interesting thread on it's own is "great old movies with good 5.1 remixes". I just saw Once Upon A Time In the West, and thought they did a pretty nice job on it.