Here is a picture of Oster A5 clippers. They are small, maybe 8 inches long. They have single and 2 speed models, I have one of each. Single speed is powerful, does a good job. I got a deal on the 2 speed used, would not have gotten it otherwise.
http://www.householdappliance.com/goldena5.html
This is what we call the "big" Sunbeam/Osters for body clipping. Sunbeam used to be the company name, Oster bought them out. Still haven't got it straight in my mind when talking about them. Mine are elderly, were Sunbeams when I got them, still call them that! Probably should just call them Clipmasters, which is the model name.
http://www.householdappliance.com/clipmaster.html
I would strongly recommend a single speed model, they are more powerful than the variable speed models, don't get hot as quick. Somehow there is a power loss with the variable speed switch. We have had both kinds, traded off the variable speeds for single speed black ones. These black ones are what we use for both the sheep clipping and the body clipping of horses, same blades.
Clipper body is the same, whether using the head and blades above, or changing it to put a shearing head that uses combs instead. Not hard to do yourself. We have done that with one clipper we have. Then we changed it back to the regular head since it works better on the sheep.
Here is a site with all the clippers, blades down at the bottom, in all sizes and shapes to fit these clippers.
http://www.householdappliance.com/oster_clipper.html
There are LOTS of other places selling these clipper models, so it can pay to shop around. Even worn or old, all the parts are able to be replaced, so finding some yucky looking clippers in these models cheap, getting them fixed, could be a bargin. Blades need to be sharp, so sending clippers and blades in for attention is part of the expense of using them. Our local guy is GOOD, fixes and sharpens or tells you they are not worth fixing.
Other clipper brands are popular too, our 4-H folks like Listers. They have a LOT of sheep, but the Listers are what they use at the shows for market lambs. They do not use sheep blades either, which is where we learned our clipping methods. Wool comes off like a hot knife thru butter. No holes in the lambs, because they are clipping a couple hours before showing!
http://www.sheepman.com/ecommerce/ecomm_product_details.asp?prodId=1517&source=cat&catId=32
We also did the "more teeth on comb, the better the cutting" on advice from friends. I think ours are 17 tooth combs, which didn't do any better on our lambs. We do pull skin taut, have non-wrinkly sheep! Still do best with the old Clipmasters and regular blades, not sheep blades.