This is a compilation of materials from Blender: Noob to Pro's "Every Material Known to Man" collection, conveniently packed into a single *.blend file, so you can append them into any Blender project.

https://secure.wikimedia.org/wikibooks/en/wiki/Blender_3D:_Noob_to_Pro/Every_Material_Known_to_Man

As of the first version, there are mostly just metals, and most rely on reflectivity to look good, so it's only the fault of the background if they look wrong in the previews.

I plan on updating this periodically, so be sure to favorite it for updates. ;)

Version 1: marble (two versions), iron, rusty iron, cotton, copper, concrete, chrome (two versions), ceramic, cast iron, bronze, brass, alloy, wood (two versions), steel (three versions), skin (Caucasian, African, brown, tan), sand, rust, rubber (two versions), moss, mirror.