BabasChess -- a fantastic internet chess client, depending on the level or desire of your son:
http://www.babaschess.net/He can play against people or computers (of varying levels) and also watch other games being played.
My son is just a casual player so this stuff is definitely over his head right now. But we do use Babas to play games over the net when the mood strikes him. If nothing else, he enjoys the IM-style chat, complete with sound effects!
If he ever decides to get serious about chess, he will absolutely love what Babas can do for him.
