We have really enjoyed "sports resort".
Many of the games we have are really similar to what you might play on a standard console in that you can sit on your butt. The sports games encourage the player to get up and move.
Even the basic wii sports disc that comes with the console is pretty good.
I got Wii Fit Plus because I wanted the balance board, but my son really likes doing the exercises on there as well.
Interesting story:
We had left for a few days over the new year for a family ski get away. While we were gone, we decided to hide the Wii in the oven (our house was burglarized last time we went on vacation, so we wanted to hide anything that would be easily stolen).
On the night we came home, my wife decided that garlic bread would be a nice side dish for our dinner and set the oven to broil..... Long story short, our remotes are completely melted and so our our RCA cables. The console is partially melted, but we were able to turn it on and eject the disc that was in there. We'll have to try it out to see if it still works.
I think I might be the only guy in America with a broiled Wii.