The fact is, DirectTV will not be carrying local channels in HD for quite some time, so you will have to settle for Monday Night Football or the other prime time channels in Standard Definition.  Unless........you have local stations in your area that are broadcasting in high def. To find out plug you address into Antennaweb.org the stations with the * next to them are digital stations and they may broadcast in high definition.  Check their website or give them a call for details.  Antennaweb will also provide you with details of what antenna you will need based on your location and signal strength.  If you live in a major city you may be able to get away with a Multi-directional antenna  but most of you, including me will need a directional antenna.  Here is my current plan

Phase I: Includes antenna, basic mounting and cabling
$63 - Antenna - 4228A Channel Master 8-Bay UHF Antenna
$30 - Cable RG 6 50ft
$20 - Chimney Mount
$15 - 10ft Antenna mast
$5   - 40ft Grounding Wire
$5   - Grounding Block

Total: $140

Phase II: Includes an amplifier and rotor to get stations from other broadcast locations.
$66 - 7777 Channel Master Pre-Amp from Warren Electronics
$80 - 9521A Channel Master Remote-Control Rotator
$9   - 75ft Rotator Cable

Total: $155
Grand Total $295

If you want to look at other recommended antennas, check out the information on hdtvprimer.com.  They offer excellent untainted advice.