For something that puts a lot of demands on the surrounds try Monsters Inc. Check out the scene named "23-19"...a helicopter flies overhead, the monsters are running around the room, alarms going off, etc.

Also, the THX intro (test?) scene puts a lot of sound through the surrounds.

If you're into music and concert DVD's then I would recommend "A Concert For George", the tribute to George Harrison. Great music and the surrounds make you feel like you're right there.