Variety of wallpaper distribution sites for high-resolution monitors
If you are using a dual display or using a monitor with extremely high resolution, you will be in trouble because there are few options for wallpaper.
So, I gathered the sites distributing the wallpapers of 2560 x 1600, 1920 x 1200, 1680 x 1050, 1600 x 1200, 1440 x 900, 1280 x 1024, 1280 x 960, 1280 x 800, 1024 x 768 sizes.
A site distributing 2560 x 1600 level wallpaper.
InterfaceLIFT: High-Resolution Widescreen Wallpaper (by ratings)
Free Widescreen Desktop Wallpapers for Mac & PSP by Steve Truett
365 wallpapers - gallery
This is up to 1920 x 1200.
Digital Blasphemy Free 3D Wallpapers
This is a maximum of 1600 x 1200.
Caedes Desktop Backgrounds - Photography, Abstract, 3D - Caedes Desktop Wallpaper - Caedes.net
Up to 1280 x 1024.
It can be used as a wallpaper of large resolution.
Flickr has more than 8000 sheets. There are many sizes, but the big ones are quite often. The minimum size is 1024 x 768.
Flickr: The Wallpapers (1024 x 768 minimum) Pool