I've just released the source files for all of my wallpapers. They're all made in Photoshop so you get the original PSD file along with any other resources used for the wallpaper. They can all be found linked in the description of each wallpaper.
I'm publishing these because I feel this is a good way to learn about how other artists do things. Also there have been many times when I look at someone else's work and think it would be great to have their source files, but no one ever publishes them. Anyway, I hope these will be useful, but if people abuse them/don't credit me I won't publish them for future wallpapers.