PowerPCDownloads
Since 7.04 Ubuntu, PowerPC downloads of Ubuntu are not available on all Ubuntu mirrors. They have been moved into the ports section of the main mirror.
9.04 Jaunty Jackalope
Desktop (Live cd), Alternate (text mode installer), and server cd.
8.10 Intrepid Ibex
Desktop (Live cd), Alternate (text mode installer), and server cd.
Kubuntu, Edubuntu, Xubuntu
There do not seem to be any live CDs for Kubuntu or Edubuntu for PPC yet, but a list of xubuntu releases can be found here:
It is always possible to install by using the server CD and then installing either the kubuntu-desktop, edubuntu-desktop, or xubuntu-desktop packages via apt-get or aptitude.
8.04 Hardy Heron
Desktop (Live cd), Alternate (text mode installer), and server cd.
Kubuntu, Edubuntu, Xubuntu
Kubuntu http://cdimage.ubuntu.com/kubuntu/ports/releases/hardy/release/
Edubuntu http://cdimage.ubuntu.com/edubuntu/ports/releases/hardy/release/
Xubuntu ???? (it should be possible to install with the server cd, and then install the xubuntu-desktop package)
7.10 Gutsy Gibbon
Kubuntu, Edubuntu, Xubuntu
Kubuntu images are at http://cdimage.ubuntu.com/kubuntu/ports/releases/7.10/release/
Edubuntu images are at http://cdimage.ubuntu.com/edubuntu/ports/releases/7.10/release/
Xubuntu images are at http://cdimage.ubuntu.com/xubuntu/ports/releases/7.10/release/
6.10 Edgy Eft, 6.06 Dapper Drake and older versions
These version can be found for PowerPC on all official mirrors