The folks at Cornell university have created a sort of platform for studying materials and textures, keeping it completely open for public contribution. It’s a big database of photos, but where contributors have isolated each material and inputted the various material properties as close as possible.

It looks a little too basic to be useful for any serious hyper-real material studies, but it’s a decent starting point for basic material properties such as diffuse and glossy intensities, roughness and colour.

OpenSurfaces
(Database download link is at the bottom, though the papers are the top are quite interesting)