Have you tried distrowatch???????

They are called derivatives or forks. Wikipedia has a good link to trace
Linux distros to their source. The best known Ubuntu derivative or fork is
Mint which is so successful that it is beginning to rival its parent.

en....pedia.org/.../Comparison_of_Linux_distributions

I installed Ubuntu 10.04. I have been thinking about
installing Kubuntu in addition to Ubuntu. Any suggestions on the proper way
to do this?

"sudo apt-get install kubuntu-desktop"

From a terminal type sudo apt-get install kubuntu-desktop or from Synaptic
search fro kubuntu-desktop or go to meta packages section to find it
manually.