Crystal Desktop Wallpaper
The direct download button links to the 1680×1050 version wallpaper. Check the Dribbble post to download the 1920×1200 version as well.
Helpful hint: Dribbble users are nice. If the license is unknown, it is usually because they forgot to mention it explicitly; not because they were being stingy. Ask nicely and they will probably allow you to use it.