This instructable covers the conversion of an RC truck into an Arduino controlled robot. My intent when beginning this project was to A) learn more about Arduino and programming B) build a reliable low cost platform to expand upon C) spend more money than I should at Radio Shack.
So if you are looking for an entry level project to cut your teeth on or a scalable platform for your wheeled robotic ambitions, I hope you find this instructable helpful and look forward to seeing how everyone improves upon it.
I conducted a search for similar instructables prior to writing this up and found a couple others (here and here) that are quite good and worth checking out as well. The main difference between my 'able and theirs' is that I used three PING sensors vice one to give our robot greater flexibility in regards to obstacle avoidance. The drawback here is of course the obvious and non-trivial increase in cost.