This website has very nice free backgrounds. When you find one you like, click it and you will get a preview of what it looks like in an image. To get the seamless one, right-click the link below the preview to save it. If you don't do that you won't get the seamless tile.

http://www.backgroundlabs.com/

To use it in GIMP, open the background, Edit > Copy, Edit > Paste As New Pattern, name the Pattern and the file and save.

Saved it. I'll include it in my gimp links section when I get my website remodeled. Thanks

great resource site! I'd love to learn how to make all of these backgrounds, but I know I'll never have the time, lol.

Bookmarked! =)
I downloaded some real nice ones for texture fills.
Brick, rocks, and wood.
It's always nice to find a free resource for free textures,backgrounds and patterns

Thanks for sharing O!

Here are a couple more i found grazing the web. =)
http://www.grungetextures.com/

and

http://urbandirty.com/