I'll give another vote for XFCE, though I haven't tried it in Linux. Works well in OpenBSD.
XFCE is very nice, but unfortunately, Xubuntu, the XFCE version of Ubuntu, is so bloated that some report that it actually runs SLOWER than regular Ubuntu. A shame.
I’ve thought of doing a custom build of base Ubuntu + XFCE to get the maximum speed out of my laptop, but it takes a LOT of time to do that, unfortunately.