I play Animal Crossing: Wild World a lot, and Mario Kart every once in a while. (In fact, anyone who plays MarioKart on wifi, feel free to PM me for my friend code if you like -- always more fun to wifi with someone you "know" than waiting for random players!)
Hubby likes the Brain Training games, and has been obsessed with Legend of Zelda (Phantom Hourglass I think? I haven't played it) for the past week or so.