For a canine, you could make it with lots of moving parts (legs, mouth, tongue, etc.) and sensors for inputs (a pressure sensor for shaking paws, sitting down, etc.). Don't make it scary, though!
Some ideas I've thrown around for fun:
- 12 CIM, two-speed mecanum
- A programmed "Rube Goldberg" machine with cRIO and a lot of I/O's
- A redesigned shooter deck for our competition robot that incorporates a tightly-packaged linear shooter
- Use the competition robot to play frisbee with kids (low power, light tosses)
Two of our team's mentors and myself are working on version 3 of a small robot controlled by a Wii Balance board, dubbed the Wi-bot. In our experience, it is a great tool for getting students (and adults) interested in the technology.