For single player, Zelda is an obvious choice. I'm enjoying it a lot...but then again, I've been enjoying Zelda since the NES days.
For your multiplayer, first don't overlook the Wii Sports that came with it. Bowling is fun as heck for multiplayer.
WarioWare is supposed to be good, and I think Rayman Raving Rabids is another good mini-game style game. Only one controller needed. Mario Party 8 will require multiple controllers, but you should really have at least two controllers anyway. It makes even games like Bowling easier when you're not constantly passing a single controller around.