Seeing that the included addon script for making grears is broken in the 2.66a version, and not finding any others here, I decided to make my own from scratch and practice with the Cycles nodes. What I ended up with, being new to Blender and node editing, was rather pleasing to me.
The gears and associated materials are yours to do with as you please. Constructive criticism of how I used the nodes to make the materials are very welcome, I'd love to know better ways to do things :)
The leather material is from elsewhere on this site; thanks to "elbrujodelatribu" for a wonderful resource!
(The preview render uses an environment texture which is not included, but doing a search for free HDRi maps will result in many available.)