If you are talking about (Free) Over The Air (OTA) reception, it's easy.
And there is plenty of free resources available.
I used OTA exclusively for HD when I lived near Seattle.
ScottMac is on target. but a few changes out here (near Seattle)
Transmitting antennas are at different headings (direction from me).
Hills and valleys make some distance charts worthless.
Top of the Hills get good signals. I am about 50 miles from antennas (not a problem), but have big hill that blocks ALL SIGNALS here. sucks.
A couple of links you can follow to find YOUR information. both are downtree, but you can find the home page yourself.
You will also find it easy to search for and build DIY antennaes.
My favorite site for purchasing is http://www.solidsignal.com/cview.asp?mc=03&d=over-the-air-tv-antennas-supplies&c=TV Tuner Cards