This Python script will help you make clay and wire renders.
A script to setup and apply materials for a wire render... It will replace your own with a clay and a wire materials, as seen here and here.
You can apply settings to all visible or just selected MESHES. Anyway, it's very easy to use.
- works in BI on meshes only
- by default it will run over all visible objects, but you can restrict to a selection
- script looks for materials by name: rename or make single user to get different wire colors
- 'mat_wire' has a z-offset option than can be used to fine tune wires display
- enable ambient occlusion or 'shadeless' option to do a fast render without setting up lights
- if it fails in default mode try selecting objects and enabling 'selected meshes'