Reference discs are considered the gold standard...the kind of discs to really show off your system.

Several have already been mentioned but here are a few:

T3...(Oh yeah!)

T2( Extreme Edition)

U-571...(the depth charge explosions are outstanding)

Finding Nemo...(the vibrant saturated colors are incredible and the surround mix is stellar, particularily when the mines explode)

Both of the LOTR's.....(both feature major-league LFE and the sweeping musical score in the Two Towers is outstanding)

Pearl Harbor...(yeah, I know about the sappy storyline in the earlier parts but the battle scenes at Pearl blew me away)

Shrek

Monster's Inc

Toy Story 1&2...(both are very good but the second one features some of the best surround effects ever, a Hall of Famer)

Ice Age

Sleepy Hollow

The Haunting...(not a great movie but the LFE throughout the movie will rattle your walls)

There are tons of others but I think you get the idea.