An awesome idea would be a fighting robot. Sure, they probably have one, but not one that destroys the other. So they can listen to you if you say "punch" or "kick" and they will do that. Maybe parts could fall off so that they know who wins. Kids would go crazy for that.
Other robots from Synthiam community

Ezang's My New Whirlybird Project For You To View
My New Whirlybird project for you to view, another Servo city ARC robot

Lars1989's Omnibot 2020 - The Next Generation
Hello community, I bought an old Omnibot 2000 from ebay and want to give him a new life with the ez-robot kit: After I...

51M0n76's Meet Arnie
HI this is my robot i call him Arnie (i dont know why) his head is on a pan/tilt joint so he can look around quite...