These Stingray bot parts were purchased second hand, because Parallax unfortunately stopped making them some time ago, but I think they are pretty awesome. Roughly 3x the size of the smaller Activitybots we were playing around with before, and DC motors for some serious speed. They're almost too fast for the ultrasound sensors' ability to let it know when something is up ahead. Here's a couple pics of Kat and the Stingray bots. Have to click on them to enlarge.
stingray_original_kat.jpg
stingray_original_complete.jpg