KDE 4
The release of the newest KDE iteration has sparked my interest in this very functional desktop environment. I stayed away from it for a long time, ignoring even Kubuntu due to my being turned off by the overample and confusing interface. But now it seems that the guys have got UI design very right with KDE 4.
The literature says that version 4.0.0 still has full of bugs, but I downloaded the Kubuntu Hardy Heron (8.04) Alpha 4 release to try and see if the bugs are significant enough to hinder a satisfactory desktop experience. In any case, I am keeping my eye on this one.