In what could be either a great exercise in DIY robotics, or a chilling vision of the future - "vexedphoenix" has documented how to build a very clever four-legged robot. It uses an Arduino-type board in conjunction with some custom pulse-width modulation circuitry, Using some balsa wood and inexpensive servos to keep the cost down doesn't seem to handicap the robot at all, in fact it moves around quite well as shown below:
The author notes the use of an accelerometer would be a good addition to help the robot consider balance as it moves along. Due to the tensile strength of the balsa wood it may not support a larger battery for total autonomy, however the use of extruded aluminium may solve that for more advanced constructors.
However for more information on the robot and complete construction advice, visit the website.