This is an example of something else you can make with an Arduino. Arcbotics used an Arduino Leonardo as a base for the controller for this robot, and this is my post about finally getting it running:
Took some time this weekend to work on my Hexy hexapod. I've been playing with this for a year or two after getting it in a kickstarter, got frustrated and put it away for a while. Had some ideas to get it to run better (mostly because of power issues) and implemented them this weekend.
It's working fantastic (well except for a few stripped servo gears) when it's wired, but wirelessly it's extremely jerky and it's missing commands. So the next steps are to replace the servo gears with carbon ones, and replace the controller with an updated one and install an Arduino as it's 'brain' to send the commands over serial so there's no wireless delay. Then I'll use a PS3 controller to control it and it should work awesome.