Pad Racer is a racing game for the iPad that lets you control your car with an iPhone. It's now a lot bigger.
You can now combine two iPads and make one large track. A neat trick, but it could really be made better as a "LEGO" style system, where 4-8 people can get together, slap their iPads down on a table and build a monster track out of it.
They'd probably need a better fix for what happens when your car hits the bezel, though, because it's always disconcerting when you lose sight of your car for that space of time.