BrainPop.com , it's not a game but has movies with a silly robot he might like. There is also a brain pop jr.
http://pbskids.org/cyberchase/index.html does he like cybercase? Some fun games here.
http://www.sciencemuseum.org.uk/launchpad/launchball/ http://www.inventionatplay.org/playhouse_tinker.htmlhttp://www.scholastic.com/magicschoolbus/Simms games might be fun, somebody else might have a website. DS was into something where he was earning point to make a amusement park. I think there is something with animal habits too.
These are mostly for a science type kid. Are you looking for an action type game? What are his interest?