Cambridge University provides a useful overview of materials properties such as the chart below.

Elastic Modulus v. Density

The tutorial can be accessed at the link:
http://www-g.eng.cam.ac.uk/125/now/mfs/tutorial/non_IE/charts.html

Joseph Klann provides a useful comparison of the leg designs for his Mondo Spider and Theo Jansen’s Strandbeest at the link:
http://www.mechanicalspider.com/comparison.html

Here is a walking machine called the Mondo Spider:

The leg of this walking machine is described in US Patent 6,260,862 awarded to Joseph Klann. Access it through the link:
http://www.google.com/patents/about?id=70YHAAAAEBAJ&dq=6,260,862

Wikipedia calls this the Klann linkage described here:
http://en.wikipedia.org/wiki/Klann_Linkage

The leg of the mondo spider has the topology known as a Stephenson six-bar.