Personally, I like Postnuke. For the longest time, skinning your site was a bit of a pain. But...someone has released a theme that seperates the code from the design. It's called AutoTheme.
Check out
http://www.portalzine.de
I've got all the mods and blocks that he offers and will hook you up if need be. Since it's GPL...I can do what I want with them ;)