Let's get right down to it. First thing to do is determine if you CAN, in fact, receive OTA (Over The Air) Digital TV. The best place to check is Antennaweb.org. Simply fill out the info it wants, and it'll give you a ton of info pertaining to your location. All channels with a (DTV) next to them are going to be the ones available in digital. This web site is very handy, but I feel I must warn you to completely disregard their pathetic excuse for an antenna selector. This function is useful to find the direction to point a directional antenna (one that receives signal from the direction you point it), but it does not give accurate recommendations on which antenna to purchase.
Now that you've found out that you can receive digital programming (Oh Joy), let's see how far you are from the broadcast tower! Roll on over to 100kwatts.tmi.net, and in the search box, type in the location of the stations that you know broadcast in DTV (thanks to antenna web). Copy down the Longitude/Latitude values, and then move over to BSexton.com to check the distance between your house and the tower. The distance for me is roughly 35 to 40 miles; Much further than this, and it gets hard to get any signal stable. Not to say that it isn't impossible to get. This fellow got just over 100 miles. He has a very nice antenna, but it's only mounted in the attic. This is a prime example of what can be accomplished. Also note the resources he used to find out his station's broadcast power.
Now that we've established that there is DTV in your area, which way to point your antenna, and the distance of the tower, we can pick an antenna!