The categories are well defined and organized. Some are unique but all are of high quality. Jezebel's Backgrounds aka Backgrounds has over 150 backgrounds which, if I don't say so myself are a cut above the usual. All original and will add that certain je ne sais quoi for any designer. I'm not interested in quantity, I'm interested in quality and an offering that will provide designers and developers with something unique.
Site also includes link to some banmners.
Site heavy on Java. John's Background Page - Site is divided into 7 categories which contain about 100 backgrounds. Netscape's Background Sampler - Site by Netscape contains about 18 backgrounds. This site contains about 200 textures of high quality. Julianne's Background Textures - A site with some thought used in its layout.