Super Smash Brothers Brawl
Some Pokemon game (sorry, can't remember it's exact name, but I think it's only for Japan)
There are probably a few I'm forgetting and there are definitely more on their way. The thing is, game developers won't have access to WiiConnect24 until the beginning of 2007, which will be in like 3 months. I wouldn't be surprised if some games get a patch that allows them to play multiplayer online, but that's just speculation.