Hello! Found some - and assembled some obligatory - texture resource sites.
CG Textures
For high-res photos of everything from A-Z. Most people know this site.
http://www.cgtextures.com/
The Pattern Library
Newly started project, but already has some cool (free) patterns that can be useful for wallpapers
http://thepatternlibrary.com/
Grunge Textures
Some great stuff in here, but highest res costs a small amount of $
http://www.grungetextures.com
Texture King
Great, seemingly free, high-res photos of concrete, wood, metal, etc. Haven't checked it out thoroughly yet, but looks promising
http://www.textureking.com
Zen Textures
Zen Textures offers a few goodies as well!
http://zentextures.com
FreeStockTextures.com
Metal textures, grunge textures, paper textures… they have them all. And if you’re looking for a specific color, you can pick a color from the sidebar and the website will give you all the textures with color you chose.
http://freestocktextures.com
Texture Archive
Yet another texture archive! Some great reference in here as well.
http://www.texturearchive.com
Resources: Personal bookmarks, and http://urlm.co/blog/2011/02/01/texture-resources/