My son just bought Wii system right before Thanksgiving. I would highly recommend it to anyone looking for a system to buy for their kids. It is a blast and you can really get a work out by playing. It's definately not a "sit on the couch and move your thumbs around" kind of game. It's a get off your butt and play tennis" kind of game. With any system, there are games to watch out for that are not appropriate for a particular age, but there are a lot of other games that are not as violent/mature to choose from.
Or, how about music? Do they like to play? Guitar, drums? Or, maybe a concert is coming up they can get tickets to? CD's
I must admit, my 20 year old son is the hardest to buy for...always has been. You have to get real creative for the guys.