Texture King is a free texture resources website. Texture King allows you to use the textures they offer in whatever way you want, except sell or redistribute them.
Textures are neatly organized with categories, available on every page on the left side.
The collection of textures available is fairly good, with around 100 textures as of writing. They are offered at 1600 x 1200 resolution. Texture King recently changed from zip file downloads to image downloads, so that should help you some more.