Fifth Element is one of the classics, particularly if you buy the "Superbit" edition.

For showing off / stressing out a home theater, I tend to go for more musically inclined releases, such as Stop Making Sense, Blue Man Group's Complex Tour Live, Trainspotting (not for young audiences), Run Lola Run, or even Rize. Pixar releases also make the short list. All the home theater geeks like the "fish tank scene" from Finding Nemo (with its 35Hz thud noise). There are also some great low-frequency sound effects in Monsters, Inc. Also good are the Sessions at West 54th compilations (link for volume 2). Those push pretty hard on using the full range of a 5.1 system.