The post for where to get images for PowerPC is currently down. Some exciting news though, due to the hard work of several community members, Xubuntu and Kubuntu PowerPC CDs are now available (or will be once cdimage.ubuntu.com returns). In addition, LiveCDs are now available

Ubuntu 9.04:
http://cdimage.ubuntu.com/kubuntu/ports/releases/jaunty

Kubuntu 9.04:
http://cdimage.ubuntu.com/kubuntu/ports/releases/jaunty

Xubuntu 9.04:
http://cdimage.ubuntu.com/xubuntu/ports/releases/jaunty