When budgeting though, make sure you allow for "accessories".
The Wii only comes with one controller, so anything you want to play against another player, like most Wii Sports games, means you have to shell out for another.
I'd also consider a charging dock, of some description, for the controllers. Otherwise you'll be up for truckloads of batteries.
Games wise.....Mario Karts is a must. Fun for everyone.
I can't recommend Sports Resort, as it's a Xmas present and hasn't been opened yet, but all signs point to it being a lot of fun as well.
The main thing to remember is that you're not getting a serious gaming machine. It's got less processing power and less graphics capability than XBox and PS3. It's a FUN console though, and the games reflect that.
Generally speaking, anything Mario baased is great value. My kids both enjoy the Olympics ones and my son loves Mario Party.