- Skinz.org: free desktop themes here, as well as themes for other applications and gadgets (iPod, calculators, etc.).
- StudioTwentyEight.com: free desktop themes for download here; really beautiful designs from nature to abstract.
- KDE-Look.org: huge variety of really cool and interesting desktop themes here.
- InterfaceLift.com: free desktop themes for Mac, Windows, and Linux.
- WinMatrix.com: you have to search for them a little, but there are great themes to be had here.
- WinCustomize.com: I just got my new desktop theme from this site. Beautiful themes and many to choose from.
- ThemeWorld.com: literally hundreds of free desktop themes here sorted by category.
- PixelGirl: my favorite place to find new desktop themes on the Web. Really unique designs here.
Note: Before downloading anything from any of these sites, please take proper precautions to keep your computer safe. Read my article Free Adware and Spyware Removers On The Web to get more information.