Although most people probably don’t need to be told, MarioKart Wii is out, and it’s loads of fun. The wheel takes a little getting used to (the first few races with it were brutally hard), but if you despise it you can always use the Wii remote + nunchuk or your old Gamecube controller.
I haven’t played all the races yet (two cups left to go!), but I highly recommend the game. Similar to the DS version (which rocked), MarioKart Wii offers 16 new races, and a full 16 races from selected past versions of the game (a mixture of DS all the way back to the SNES). Although the co-op goodness of Double Dash is no more, it’s still a great time with a friend, and also offers the ability to easily play online with up to 12 other people. Owning MarioKart is all but compulsory if you own a Nintendo system, so definitely give it a look. (And at the time of this writing, Wii Wheels on Amazon are only $10 as opposed to the normal $15, which is a bit more reasonable.)