I used the bricopacks at crystalxp and loved them, especially the Vista Inspirat 2....it is gorgeous. and looks a lot like vista. But i just got WindowBlinds and it is much much more powerful because it makes use of your video card. It also has more skins which you can find at www.windmodify.com
or deviantart. (WindowBlinds normally isn't free though.
There is a problem I have though with both bricopacks and Windowblinds....neither will completely skin Internet explorer, so i end up with ugly light blue tabs in explorer against a black background.