If you are looking for a dual monitor wallpaper (2560×1024) in one of the following categories then dualmonitorbackgrounds.com is the site to see.

Abstract

Animal

Astronomy

Celebrities

Computers

Crafted Nature

Gaming

Industrial

Macabre

Microscopic

Mobile Technology

Music

Nature

Popular Culture

Science Fiction

Sports

Vehicles

World of Warcraft HD Wallpaper by Storke has 24 High Def World of Warcraft themed Wallpapers, with resolutions as high as 2400 x 1350. Great site!

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.