[Der_Einzige]

Kubuntu with "Plazma" was the most RAM I have ever seen a Linux distro take at idle. Xubuntu was a breath of fresh air in comparison and had far fewer weird UI bugs. I don't recommend kubuntu for resource constrained systems.

[zamalek]

RAM/resource usage has been steadily decreasing for Plasma for a while, and has basically reached XFCE levels, so I suspect your information may be out of date. On my system it's currently using 250MB. Xubuntu is a great DE recommendation, though.