I adopted an ACD (Australian Cattle Dog) from a local shelter in July 2010. He was nameless for weeks. I came up with Roo, like suggested above, and also, Kanga, the mother and son characters from Winnie the Pooh.
Roster was my favorite name for a while because he would 'herd' all of his toys into a straight line in the back yard as if he was about to call the roll. Then, as I watched my 2 month old ACD springing through my back yard, I thought: "JOEY!"
As you may know, Joey is a vernacular term used in Australia to refer to baby kangaroos still in their mother's pouch. It is the perfect dog name for an Australian Cattle Dog.