So many great films to choose from...(in terms of surround sound at very least..)
Star Wars Episode 1: The pod race is truely fantastic, great sound, deep bass, brilliant sound positioning
Flight of The Phoenix: Plane flying through a sandstorm, this will give you speakers a wonderful test!
Fight Club: Near the beginning, where Ed Norton is in the plane which gets hit, the sudden rush as the cabin depressurises, is truely phenomenal!
Event Horizon: Right at the start, massive bass as the camera approaches the space ship, amazing sound positioning as we see various items (including a ticking watch) floating about inside,
The Fifth Element: When the Diva is singing, whack this up on a decent system and it sounds absolutely amazing!
Terminator 2: Great positional sounds during the future wars scenes, amazingly audio throughout, especially on the DTS track
Pulse: A little known Horror film which near the end features a room full or servers, the bass pressure of these scenes is something quite incredible
One Hour Photo: Some brilliant 'fear register' bass effects that are lovely and subtle, a real test of a decent sub....
A.I. : Again some wonderful subtle and really low bass that only a decent system will produce.
That's probably enough to be going on with, but with a bit more time to think I'm sure I can come up with a lot more.
Valve