Homerun Battle 3D is a very popular game and features online head to head, via wifi or a regular data connection. Check the recommended games sticky at the top, it should include it and many other games.
Carrom3d is a 3d billiards game. Pool and such, like 9 ball, straight, 8 ball... It is pretty sweet gameplay however there is no chat in the online multi-player because they worrie about language which is ^%#( lame... haha