Are there any multiplayer cross platform games?

So pretty much my buddy just got his first smartphone, a Droid. I was wondering if there are any multiplayer games that I can play on my 4S and he can play on his Droid that we can play each on in multiplayer.

The only game I have found that can do this is 'Words with Friends' and I think 'Shadow Era' can do it as well. I didn't know if you guys knew of any others.