I started one of the threads that the pp posted. We have the sports games that come with the Wii console, Wii Play bundle (you get an extra remote and games) and Mario Kart. Target was out of extra steering wheels when I initially bought Mario Kart so DS1 is getting it for Christmas. Mario Kart gets the most play at our house by far. DS and his friends play that one frequently. That will get you started nicely unless you just want to buy more now. I am debating getting the Winter Olympics game for DS1 for Christmas but he really doesn't need any more gifts.
Have fun with it! We've really enjoyed having it.
Mom to Two Wild and Crazy Boys and One Sweet Baby Girl