One thing I can think of is finding demo disks, as those will have 15-minute blurbs of several different games apiece.
I would suggest reconsidering SoulCalibur as that's a great game for a demo, both because as a fighting game, games are quite short, and a person can still easily get into it via button mashing.
Beyond that, I'd probably suggest:
At least one fighting game (If not SoulCalibur, then Marvel Vs. Capcom or King of Fighters)
A Burnout game (2 or beyond)
Cel Damage
Crimson Skies
Crash: Tag Team Racing
Fuzion Frenzy
The Simpsons: Hit & Run
A SSX game
Star Wars Battlefront (1 or 2)
A Tony Hawk game
And if you really want to throw people for a loop, Steel Battalion with its controller. Granted, it's not the most demo-able game, but it would make it the center of attention.