Wall Street Journal: One-half of the 24 million households with HDTVs don't actually watch high-definition programs because they haven't obtained the necessary hardware from their cable, phone or satellite operators.
If you are considering an HDTV and you don't have a set top box from your cable company, be user to get a QAM tuner. This lets you see unencrypted HD content from the networks like NBC, CBS, FOX, and ABC. Maybe even other small local channels. You have to look for QAM, not every one has it. They'll advertise ATSC but that is over the air and not everyone can put up a big antenna on their house. Those unencrypted channels are part of basic cable too.
Of course, this doesn't let you record that content, you'll need a digital tuner in the device you are recording to or an external tuner like from your cable company. But at least you can get at least some form of HD on that expensive TV.