I love Nintendo 1st party franchises -- the games don't come fast, but they are always great games.
Other than that, I pretty much only use the Wii for party games, like Dokapon Kingdom, which its actually really great for, and SNES RPGs, which I have fun replaying from time to time. RPGs, unlike other genres, never really get too old to play, despite aged graphics, etc. IMO. =)