You can't go wrong with Mario Kart, to be sure. Its certainly not hard core racing, but its great fun with power-ups and payback that have always left our friends and family laughing and shaking their fist at each other(all in fun, naturally). We also have the Speed Racer game from a few years back and its crazy physics are also kind of loopy. You get to unlock different tracks and competitors the further you move along. Not sure its for everyone, but we enjoy it.
My biggest disappointment is that there is yet to be a decent review for a Wii Need for Speed title. That's a shame, because I really enjoy the NFS franchise on my PS2.