On February 17, 2009 the analog signal will end and the digital signal will take over. By March of 2007, every TV sold will come with a digital tuner that will allow you to receive digital broadcasts.
Metropolitan Home has a shopping guide and explains that HDTV comes in a variety of flat screens including LCD (up to 60 inches) and Plasma (wide viewing angle and 40 to 80 inches), rear projection, direct view and front projectors.
Then there is the audition.
Before you leave home, measure the viewing distance from your couch (sofa) to your current TV. At the store, stand the same distance from the screen. You should see a seamless picture without visible lines (or Pixels) in the image. If you want the TV to be viewable over a wide area-say from the kitchen and the family room-walk to the far sides of the screen to see if you have a good view off-angle.Ask to see both HD and standard programming.
Consider bringing a DVD to see how it handles content that you know.
If the price seems too good to be true, it probably is.
Picture Quality is subject to three versions:
SDTV - your least expensive option. These sets generally measure 32-inches or less and picture quality is on a par with DVD (480 scanning lines).Remember: 1080p
EDTV - better resolution than SDTV, but will not give you full benefit of HDTV
HDTV - best of the best. While more expensive, they can fully display all types of high definition (720 by 1080 lines of resolution).
You may need new furniture to accomodate your new TV. Look for a cabinet or wall unit with a large enough opening for your new TV. You might make a cardboard template of your cabinet when shopping for a TV or vice versa. Allow 2 inches around the cut out for ventilation.
Look for furniture that has wire management solutions built in. Holes in the rear accomodate wires and provide ventilation.
Make sure the cabinet allows the TV to sit flush with the front of the shelf so it can be seen from all angles.
Landfair Furniture + Design Gallery features Hekman, Hammary and Nichols & Stone that have styles specifically geared to flat screen TVs. Hekman has consoles that conseal the TV until you are ready to view your program.
Bev & Mike
UPDATE: Kevin Hunt has further thoughts about HDTV in What You Should Know About HDTV, From A Guru