The company I work for sells off-air HDTV antennas, and business has been really booming for this stuff.
http://www.antennaweb.org is a good start to research the "type" (color code) antenna you would need for OTA HD.
What do you mean by "off-air?" These antennas don't work with traditional broadcasts?
In addition to our new tv, we also bought speakers, subwoofer and an audio receiver. VERY complicated stuff (for an old fogey) and I'm still trying to figure it all out. One of the things I notice is that when we are in "tuner" mode, reception is not that good with the included antenna. Will these OTA HD antennas help us with that problem?