If you will regularly play with other people, and want the Wii to be social gaming, I’ll echo the recommendations for Warioware, Rayman Raving Rabbids, and Mario Party 8, all of which are minigame compilations, with many interesting ways to use the remote, sometimes lasting only a moment or two per minigame. Of the three, I’d recommend MP8, which has a good overarching “board game” beyond the minigames.
On the horizon is the Wii killer app: Super Smash Bros Brawl. Lighthearted one-on-one (well, up to four players) fighting game that will have all sorts of cooperative and competitive fighting modes. And online play.