Backgrounds Archive
Database of high quality tilable backgrounds that can be searched by brightness, color, category and file size.

Art-Tlc: Animated Backgrounds
Includes lots of animated backgrounds for your web page.

Background City
Includes backgrounds in a number of categories, as well as several background themes. The themes include holidays, birthdays, sports, and more. Also allows you to view numerous colors of text over each background, a great way to help you decide what you like quickly.

Backgrounds by Carel
Lots of really nice, free backgrounds!

Texture Station
Some backgrounds for your web site.

The Web's Worst Backgrounds
Includes some pretty wild animated backgrounds. As the title says-- you may not want to actually use the backgrounds, but it may be worth a look if you like wild animations.

Wonder Backgrounds
Includes numerous backgrounds in a variety of categories. Backgrounds for holidays, nature, patterns, birthdays, and more.

ZettWeb
Has lots of images for backgrounds and/or multimedia design. Every week there is a new high resolution "wallpaper" (640,800,1024,1280,1600 x 480,600,768,960,1200 pix) Currently about 1500 images 640x480 in different categories. All pictures are compressed with jpg.