I use for playing lots of multi-player games.

When my friends come over, we could just get together and play games together

Try these:
Bump bump
ICE Rage
multiponk
Bop it
GameRoom
wheel of fortune
OSMOS HD
Foosball HD
Flight Control HD
FIFA
Metal Slug
Air Hockey
Air Dogs
Blokus
Pictureka / Time Geeks

Thats pretty much what I can remember on top of my head.
Also some single-player games work great on the iPad that aren't on other platforms...