Rovera 2W, $175
The Make: Rovera robot line is a great way to get started in serious hobby robotics. The 2W version comes with all of the parts you need to make a two-wheeled robot that can serve as the foundation for all sorts of robotic experimentation. The kit comes with the book Make an Arduino-Controlled Robot, by bestselling author Michael Margolis (author of the Arduino Cookbook). The book carefully walks you through the building of both the 2WD and 4WD Roveras, how to program them, how to expand upon them, and more. Finally an Arduino-powered robot kit from MAKE!