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.

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.