if you have photoshop and illustrator, you can make similar ones yourself. fool around with the tools (though not too much). Basically, it's vector art with a little effects...
One of my absolute faves regarding desktop backgrounds is Fracture: http://macupdate.com/info.php/id/7859.
"But it's a screensaver, and I want desktop backgrounds!, you say.
Well, hold your water, sir or madam; while Fracture IS a fractal generating screensaver, it allows one to save any of the created fractals and use them for desktop backgrounds (or any other use).
Try it out. You can get some mindblowing images!