Welcome to AVS! Feel free to ask us any questions you might have -- You should be in a excellent spot for OTA HD/DTV reception from Dayton/Cincinnati. 2nd post of this thread has info on the Cincinnati stations, you can find info on the Dayton stations in Dayton thread.
I wouldn't think you'd need a large antenna from your location for Dayton/Cincy -- Antennaweb's predictions seem to be much more conservative than it used to be. I'd think you would have a good shot at it with a small/medium sized (directional) VHF/UHF combo antenna - Radio Shack, Channel master(Lowe's has some of their stuff), and Winegard are a few you would want to look into. Even a UHF antenna, such as a CM4221 *might* do the trick for you, even though ABC Cincinnati HD is on VHF 10(rest of Cincinnati/Dayton Digitals are currently on UHF).
A rotor would likely pretty much be a necessity for Both Dayton and Cincinnati, but you would probably want to try a little "manual rotation" first to see how it works --- Or -- You could use seperate antennas(on seperate feedlines) For Dayton/Cincinnati and use a A/B switch near the receiver to select between the antennas -- I do this here (I'm North of Middletown, BTW) and it is more convienent than using a rotor -- And -- as far as the 2nd cable run to 2nd antenna goes -- with a rotor, you would need to run a 2nd cable (the rotor control cable), anyway.
As for a preamp -- You probably won't need it, but then again, if you have a long cable run, or are going to be splitting the signal to many devices/TV's a preamp might be benefical for you -- I'd try it w/o a preamp first and see how it goes, though -- Sometimes a preamp can hurt more than it helps, or vice versa, and you probably don't want to get something too "high gain" from your location ... Winegard, Channel Master+Blonder-Tongue make some nice mast mount preamps, RS preamps should generally be avoided as they generally overload quite easily ...
You might find this link handy, as this place carries antennas/preamps/etc/etc, in all shapes and sizes, and generally provides good specs on the equipment :http://www.starkelectronic.com/allant.htm
Oh -- By the way -- Hopefully a helpful hint antenna wise -- What works good for Analog reception works good for Digital Too or vice versa -- RF is RF, both Digtal and analog use the same frequencies/channel (TV VHF/UHF bands - Ch 2-69) no such thing as a "HD" or "digital" antenna.