Dorpers are popular around here and are easy to find (we're not in sheep country so there isn't a huge selection of breeds to choose from). I practice on a mostly dorper flock and you can't beat their temperament. Here's some of the flock we practice on with their lambs:
Barbados Blackbellies are another popular sheep for herding. Their small size appeals to me, as well as their coloring and they are a hair sheep. I'm not so sure about the rams and their horns though -I guess I don't need a ram (or not yet anyway).
While researching barbados, I stumbled upon "Painted Desert Sheep" These are a breed of sheep developed in Texas by crossing Mouflon,Rambouillet, Merino with Blackbellies. They are built like a barbados but have "painted" markings like a paint horse. I have decided this is the breed of sheep I'd like to try.
I have scanned the craigslist postings and have located a farmer with a herd of barbados/painted desert sheep priced reasonably in Kingston, OK so I plan on taking a look to see what he has on Monday.