Go Nintendo posted an article which stated one of the main worries behind the Wii; if the games (mainly Wii sports) and the controller will be enough to keep non gamers (family, casual gaming friends etc.) interested in the Wii.
While the concern is valid, there shouldn't be much to worry about because Nintendo already has planned games that take Wii sports' appeal further.
First is Wii music (aka, the conductor demo at E3). You have seen how in all the Wii trailers they show at least one person being a conductor. This is a game that can easily attract lots of people in, especially if you're conducting skills affects the overall performance.
In the US we will get Wii play in January. That should provide hours of party game fun.
Big Brain Wii should be good as well, especially if it delivers multiplayer the same way the DS game did (which was VERY fun).
Wario ware Wii should attract some people in, despite its niche hardcore gamer appeal. My sister and niece LOVED Wario ware touched and they are casual gamers, so there is a good chance casuals will enjoy Wario's unique brand of gaming.
And finally, if the recently announced Wii health pack is the talked about aerobics/health life game, that should attract lots of people in (especially female gamers).
Oh yeah, don't forget Animal crossing!
I'm sure there are other games I am forgetting, but what I am saying is that there shouldn't be any worries regarding the lasting appeal of the Wii beyond Wii sports because there are plenty of games in the horizon that should further enhance the Wii's performance.