The 4 below are my favourites. You can see the rest here.
On a personal note I've been using the Wii daily, sometimes twice a day. Favourite activities so far are ski-jump, slalom, hula hoops and balancing games (tilt table and tightrope) but I am starting to get into the yoga, step and jogging. It tells me I've lost 0.4kg in the first 2 days but that could be due to natural daily variation. The boxing is tough: I can only manage 5 or 6 minutes before collapsing onto the sofa and watching the opponent beat me until my head falls off.