Oh yeah, Wii also has full backward-compatibility with Gamecube games, try to find some cheap ones in pawn shops or eBay...

You'll need a nunchuck if you want to play a game that requires analog movement with another person (with another Wiimote, of course), and for MotionPlus capability you'll need MotionPlus. If you want to play certain games in the classic downloadable library, you'll need to buy either a Classic Controller or a GameCube controller. Other than that, you should be fine.