Here's the links to some previous posts:

Board games-
http://giftedissues.davidsongifted....cs/26911/Great_board_game.html#Post26911

Wii games-
http://giftedissues.davidsongifted....mes/Search/true/Wii_games.html#Post74315

My kids liked board games but probably preferred puzzles. If you are interested in that sort of thing I can recommend the following:

Rush Hour games - they are available as an online game or as a board. Lots of difficulty levels and challenging. Also has different versions e.g Safari.
http://www.puzzles.com/products/rushhour/rhfrommarkriedel/jam.html

Wasgij jigsaw puzzles- these are great fun and also challenging.
http://www.gamesparadise.com.au/category.asp?cparent=10&cid=173

PS. Safari, as in African not Mac. LOL.