So I got my heart rate monitor in yesterday and have been trying it out with Wii Sports. I started out with slow games so the faster paced games wouldn't effect the heart rate too much. I played about 10 minutes on each game and this is the calorie burn:
Total calories burned for 50 minutes of play: 227
I guess if you want to get a good workout in play tennis or boxing. But, I think we all knew that already.
Edit: btw, I let my heart rate return to normal between each game.