I don't know about Antenna or Satellite, but if your going with cable -
If you don't have a digital tuner built in, you will need a tuner box. Most new TVs come with an option called CableCard. With it you won't need a seperate tuner for the extra HD channels you pay for. But you won't have the interactive TV guide, or pay per views through the remote control.
But in no way are you done there. If you plan on using a tuner box for analog signals (Channels 2-78) they will look like crap. You're HDTV displays a higher resolution, and doesn't know how to fill in the missing pieces. HDTVs that have a built in RF tuner handle it a bit better but the image leaves a bit to be desired. In 2006 this type of signal is supposed to no longer be used anyway.
What you should do is look at your cable company's website and the features they offer in your area. Decide which features you'd order, and make the TV decision based on that.