Texture Web Sites

Not sure if you know this one. I'll post anyway.

http://texturelib.com/

For a list of many free texture sites see http://arnokohl.wordpress.com/2011/03/03/texuren-1/ and http://arnokohl.wordpress.com/2011/03/06/texturen-2/. The links are commented (though in German only)

We have a large number of free textures for free download and commercial as well as personal use in the Vintyri (TM) Cartographic Collection on our website. The material all is released under the Open Game License 1.0a.

http://www.vintyri.org

Today on the Official Google SketchUp blog they featured A Treasure Trove of Textures with a link to an article on John Pacyga's SketchUp For Landscapes blog featuring links to a ton of sites with seamless textures that can be used with SketchUp, Photoshop, GIMP, CC3 and more.

Bricks, Buildings, concrete, effects, fabric, wood, nature, rock, water and wood

Not sure what the licensing requirements are:

BEST FREE RENDER TEXTURES

Rendertextures' license is quite generous. It can be found at this link: Terms of use « BEST FREE RENDER TEXTURES

In short, they only thing you really can't do is resell the textures themselves. Selling work created with them is permitted. You can even directly post the textures to other websites as long as there is a link back to rendertextures.com and they are attributed as the author.