I'm having too much fun with Arduino.
This little dude is pretty simplistic. 2 continuous rotation servos in the back control the rear wheels independently. Another standard servo rotates the Ping sensor on top to check for collisions. If an object is found in front, he'll look around for another way out. If there's no way out, he'll back up and check again. I also added a bright white LED up front for fun.
I built it using one of those Radio Shack project enclosures and a bunch of Erector Set parts. I'll get some video of him driving around soon.
The catbot would've been fun, but I had a hard time finding an electric water gun that didn't leak. I didn't want to risk burning out my Arduino, so I moved onto the next project. I'll probably use this as a base for my projects for a while. I also ordered some tank tracks and a dual-motor gearbox, so the next robot should be a bit quicker than this little guy :]