Just a few points to make in the interest of clarity (and, of course, fighting ignorance). I know several of these statements were made by others, above, but I want to add emphasis.
The move to the digital standard (currently scheduled for 2009) will not obsolete anyone’s TV. The few TVs that are still being used solely for watching OTA analog will merely need an inexpensive coverter box.
Digital TV is NOT the same as high definition. All HD is digital, but not all (or even most) digital is HD.
There is no such thing as broadcast 1080p. All broadcast TV is either 480i (standard definition TV), 720p, or 1080i. Do not expect to see 1080p broadcast anytime soon, or perhaps ever. Because of this, I really don’t expect resolutions higher than 1080p to be common in consumer displays for a long, long time.
The two HD standards, 720p & 1080i, are essentially equivalent, though each has its strengths and weaknesses (e.g. 720p better for sports, 1080i better for nature programs).
All HDTVs will convert incoming signals of any standard format to their native format for display. No need to worry about getting the right one - a 720p HDTV will display a 1080i source just fine and it will look great.
A 1080p TV will not necessarily look better than a 720p TV, other considerations being equal, unless you have 1080p source material (Blu-Ray or HD DVD or computer).
And. lastly, I have to defend my favorite display technology due a a false statement made by Drum God that DLP is only available in 720p. There are plenty of 1080p DLP TVs. The next generation DLP TV with LED light source and 1080p resolution will be my next television (I currently have a 43" Samsung 720p DLP HDTV and enjoy it immensly). HDTV is unbelievably better than SDTV - I highly recommend taking the plunge.