Last year I replaced my cable box with Tivo units and one of them is OTA only. I bought an HD Digital amplified antenna and mounted it to the roof of my home. I get better reception now than ever with cable or Dish. There are considerations in selecting an antenna, such as directional or wide area depending on where the stations are broadcasting from. Where I am at they are all in the same direction so I went with a directional to get the best signal. There are websites where you enter your zip code and they give you directions to the stations. Click on the links below to take you to the web sites.
Adam Savage has a "How To" posted on his website that may help.
How To Get The Best Reception With Your HDTV Antenna - Tested