Plasma Design 
High quality original wallpapers created by Rob Roundtool. Definitely check it out.

Caedes 
A gigantic site where users submit their own photographs as wallpaper. Some really high quality work here

Styleboost 
Some very striking wallpapers here at styleboost, mostly macro shots.

Gaia Dream Creation 
A wide variety of wallpapers, free to download

Picture Correct 
A good collection of wallpapers and some useful photoshop tutorials

Digital Blasphemy 
An amazing collection of 3D Wallpapers, created by Ryan Bliss.

Free PC Wallpapers 
A very nice collection of wallpapers

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