Depends on what you want to show off. If it's sheer thrust of the LFE and subwoofer, then U571 is a classic with the depth charges. Super 8the train wreck scene is another great demo for that. An unheralded dark horse is the Tom Cruise war of the worlds. My goodness, the bass there is earth shattering (no pun intended).
For nuances and surround effects, A agree with Transformers and will add the Star Wars movies, Lord of the Rings, and the Marvel movies like Avengers, Thor, and Iron Man. Surprisingly, Avengers isn't an LFE demo-worthy movie like the others. Some scenes in Thorlike the throne room and Ice Giants battle scenes are great.
And last but not least, don't forget the home theater classic demoThe Fifth Element.
There's lots to enjoy :-)