My first choice is the AR platform which is -not- what you are looking for, but my second choice would probably be a Saiga .223 because of price and the fact that a .223 AK clone will fetch you more but without the minor improvements the Saiga has. If pure cool factor was all I wanted I'd get an AK in .223. My next choice would be a mini-14, and then after that I would look at the Kel Tek .223.
All else fails all the big companies out there sell some variant of their rifles in an auto-loading config however unsure of their caliber offerings and if they will meet your expectations.
Edit: I realize now that you weren't specifying "budget".
Last edited by Tangentabacus; April 30, 2013 at 10:13 PM.