Zuphoria – Oeuvre is an impressive collection of wallpaper images. The images are categorized as:

3d Glass
Abstract
Fantasy [Dreams]
Fantasy [Gurls]
Gothic
Natures Force
Space
Zeetha
Disney Classic
Marvel Comics
Simpsons

Today they have over 1000 images to choose from.

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!

I was looking for an image on google image search this morning and found that they had added huge image searchThanks google!

The European Homepage for The NASA/ESA Hubble Space Telescope hosts an impressive array of awesome (truly awe inspiring) images and wallpapers of our universe.
The images are formated in 1024×768, 1280×1024, 1600×1200.
My favorite part is the High Def videos that are available on the site. They have 720P and 1080P videos for download.We are very excited [...]

Desktop Pictures hosts a lot of great images in the following categories.

Scenic
Florida Beaches
Abstract
Clouds
Flowers
Colorful Leaves
Haiku Letters
Black and White
Expressive Leaves
Holidays

Many are available in 1152 x 768, 1152 x 864, 1152 x 870, 1280 x 800, 1280 x 854, [...]

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.

Professional Wallpapers hosts a few HD images in a number of different formats. including 2560×1600, dual monitor, HDTV and PSP/iPod formats. Nice work.

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.

Plasma Design has several large 4:3, 16:9, dual monitor wallpaper and 30" Display wallpaper designs. They have 3 flavors Aqua, Landscapes and Abstracts. Membership (£7 fee for lifetime membership) is required to access their collection which consists of over 200 images.