Lost & Taken regularly posts high-quality textures–completely free for personal AND commercial use. Most texture collections are conveniently packaged in .zip files for easy downloading.
“Lost and Taken was created . . . with one intention: to helps designers by giving away the best free textures available. To this day, Lost and Taken textures have been viewed tens of millions of times and have helped thousands of designers accomplish their jobs a little easier and with more beautiful results.”