You want a movie that tests your surround? Try U-571 using the DTS track. If you crank the sound up on this movie, I can guarantee that it will pretty well test the limit. If the depth charge attack isn't causing the walls and floor to rattle......something is wrong. The movie tests your intelligence at the same time.....and I don't mean in a good way.
Hmmm.....I would single out LOTR: FOTR Ext Cut in DTS ES 6.1, Star Wars Ep 1 and 2, Saving Private Ryan, Superman, Cast Away DTS and....Das Boot (Superbit) which I just finished watching this evening;its DTS track is splendid!!!
Here's one I can recommend to show off your surround sound system: Atlantis: The Lost Empire Collector's Edition.
Be forewarned, though: the opening sequence could blow out your speakers. Later in the movie listen to how sound editor/designer Gary Rystrom masterfully places the sound effects in surround sound mode, especially in the quieter sequences.