Illumination by Daniel Parnell
This one looks really
snazzy. It claims to be a true theme system for
Windows, with
freeform skins and eventually every feature
WindowBlinds has. Oh, and it's open source as well. Development is coming along well, it was updated just recently at the end of June.
http://www.geocities.com/SiliconValley/Park/6797/illumination.html
http://sourceforge.net/project/?group_id=4064
http://www.deskmod.com
http://www.skinz.org
http://www.geocities.com/SiliconValley/Park/6797/macos_pic.jpg
http://www.geocities.com/SiliconValley/Park/6797/download.html
Also see WindowBlinds, eFX, Chroma, CustomEyes, Daya.