Surprised no one mentioned the Raving Rabbidses! The second one is especially fun, since it's more four players simultaneous instead of taking turns. But then again, the first one did have the cow tossing...
And Brawl, Guitar Hero III (and soon IV, oh yes, that will rock), and MKWii.
That Dokapon Party thing seems like fun too, will check it out once it's released.