So here's a quick poll/pooling of all our favorite materials/textures resources.
Where do you get your textures/materials when you need something that the basic pack doesn't cover?
Me?
http://images.google.com with a few advanced search options for file size on, usually. I can't see spending money on anything at TurboSquid, though it's tempting...
I've also found some good resources at
www.deviantart.com which is a digital art site (warning... not entirely work safe) that caters to 3d decently well, with a whole section devoted to 'resources'
Other than that... when doing my general browsing, I scavenge from time to time...