Here's a site that has a very good collection of high resolution and FREE textures. All of the textures where taken by the sites author so there's no question of ownership. Animals, furs, wood metals and many more. The animal pictures are good enough to use for reference material as well.
Many times there are hidden terms what free really means. From the website: "You may not sell or distribute any of these textures, use of these textures is only allowed under the following conditions: Private or commercial use in 2D or 3D computer graphics. Selling 3D models bundled with modified versions of the textures is allowed"
See the license for further details and FAQs. There are also a couple of nice tutorials for Photoshop that are worth checking out.