XFCE – XUBUNTU
First time I installed xfce on my laptop I was surprised with how light and stable it was. I have been using XFCE for more than 2 years now I would have to say that its great. I would strongly recommend it specially if you don’t have a really powerful machine like me. To customize it the way you like its obviously a little different from Gnome but once you can used to it you would see how easy it is. Here is a screen-shot of my desktop:
