Use Bitbeam for your robot's skeleton!
Bitbeam is LEGO Technic-compatible and awesome for building robots and other contraptions.
Each Bitbeam is an 8mm x 8mm square beam. Holes are 5.0 mm in diameter and 8mm apart from each other -- just like LEGO Technic.
The advantage of building your own Bitbeam parts over LEGO is that 1) the materials are cheaper, 2) you can make parts in sizes that Lego doesn't make, and 3) making your pwn parts is fun!
The original bitbeam design was meant to be cut with a laser cutter. The current version is meant to be made with a 3D printer.
Download the bitbeam-beam.scad file and open in OpenSCAD. Specify the length of beam, compile, render, then export the STL file. Import the STL into a slicing program (e.g. Slic3r), then print on a 3d printer (e.g. Lulzbot, Makerbot, etc.)
I'm blogging how to create and use bitbeam over at http://bitbeam.org. I've posted YouTube videos of the the bitbeams being cut by the laser. More, better, awesomer instructions will come soon, I promise!