Well, when you get bored of all the other games you got, you have to at least give Mario Kart Wii a try. Easily one of the best games on the Wii.
I've lost weight with the help of Wii Fit too, but I mostly just use it to monitor, not to actually exercise. I do the occasional exercise with Wii Fit, but I find that since you can't create a routine that runs through the exercises without pausing it doesn't give a very good workout. There are a few exercise games in the pipeline that look like they'll be way better. Hopefully they don't botch them, and they actually create a decent product.