Steampunk Wallpaper is awesome. I just saw this on Boing Boing.I love the firefox logo with the stitching on it.Check it out.

MacDesktops hosts hundreds of great Hi-Res wallpaper in dozens of Categories. Hours of browsing fun here. I love the My preferences settings to show you just the sizes that you need. Great feature!

wallpapers (1024×768 minimum) is the mother load of high res flickr groups. It is chock full of images tagged with wallpaper at a minimum resolution of 1024×768. 36,669 images and counting. This will take a while to go through.

desktopography is an exibition, a showcase of nature themed desktop wallpapers created by designers worldwide. This site is awesome! great visuals and great music! Lots of great, hi def and large format wall paper and all around great design. Check them out.