Nintendo DSi

YOu can't go wrong with any of the first party stuff. Mario Kart is a big hit.

The zelda games are fun. If he can read well, one of the Pokemon games would challenge him (at least time-wise)

Scribblenauts is pretty sweet. My oldest girl is just turning six and really likes it. I think it's also helping her learn how to spell. They also like Animal Crossing... even my 4 year old will play that and just walk around talking to people.

if you haven't bought them yet, Amazon is having a sale today, and I believe Target has dropped the price in store to around 127(?). I have a suggestion for a 6 year old - depending on whether they're boys or girls - the Diego and Dora games have been a big hit for my girl's (now) 7 year old. He was able to play the games on his own and figure them out. They're fairly simplistic, but good, accessible experiences. One game you might want to get for you is Picross 3D. I find it fascinating. I think it's typically $20. What you don't want to have happen all the time is the kid coming over to you to get him/her past a section. Sure, once in a while is fine, but I think the value of games at a young age is to teach logic and problem solving skills. Keep them close, but don't be too quick to get them through.