AntennaWeb is a very good resource, as has been mentioned. However, you may not need as much antenna as they recommend. I certainly didn't. Of course, YMMV.
For my location to receive the UHF digitals (they broadcast in very low power in Denver), AntennaWeb said I needed:
Outdoor, Large Directional, with Preamp (i.e., a
"violet zone" antenna).
However, what I already had installed, and which works perfectly (for me!) for all these digital stations is much less than recommended:
Channel Master CM3016, inside attic mounted (with foil lined siding), medium directional, no amp, aimed 50 degrees west of where it should be.
I didn't intentionally point the antenna in the wrong direction ... it's pointed where the analogs broadcast from. This is where the digitals will eventually be broadcast from too, come 2009. But for now our digitals are low power only, broadcasting from temporary facilities elsewhere.
A very good website in Canada has a nice FAQ on OTA antennas and reception:
OTA Forum Knowledge Base & FAQ - Digital Forum
Also, go over to
AVS Forum -> Forums -> Local HDTV Info and Reception -> the first sticky thread "United States THREAD INDEX" and find the thread for your local area to see what your neighbors are using.
It appears that for UHF only (maybe some upper VHF as well), you see
CM4221 and
CM4228 recommended frequently. Also the
DB4. Moving to a Yagi style antenna, the Radio Shack
U-75R pops up frequently too, probably the combination of it's reported good performance and ready availability locally. I do not have any personal experience with these particular antennas. I found out about them by doing research. I've only used my attic-mounted CM3016 which works perfectly for me, but might not be a top recommendation in general (probably depends on your area though).