If, like me, you're totally mystified by all the high definition tv jargon, here's a brief article that lays out the basics pretty well and also makes some recommendations if you're considering a purchase. Here's the key graph:
First off, let's tackle what High-Definition means. A television works by painting an image over and over again, usually around 60 times per second. If half the image's lines are repainted every time the screen refreshes, it's called an interlaced scan technique. If the entire picture is repainted every time the screen refreshes, it's a progressive scan technique. A regular television displays a picture that's made of 480 lines from the screen's top to bottom.
The high-definition threshold begins when the number of lines shoots up to 720, packing in more detail for those sharp "I-can-actually-see-the-guy's-skin-pores!" details. Right now, the zenith of high-definition capability you can buy is 1080p-1080 lines, progressive scan. Critical viewers prefer progressive scan for its smoother look when watching content that packs a lot of motion (like sports), mainly due to the fact that you're seeing twice the amount of pictures per second (frame rate) as you'd get with interlaced scan. The only problem is, unless you're playing a game on a PS3 or feeding content through a high-end video card on your PC, there is no actual 1080p content available for your tv. Weird, huh?
High-definition cable is piped in at 1080i and high-definition movies are filmed at less than half the rate your screen is repainted at (24 frames-per-second)...and neither of those standards are likely to change anytime soon. Having said that, if you can still find a 1080i tv (1080 lines, interlaced scan) or you pick up a 720p model (720 lines, progressive scan), you'll be satisfied. As a matter of fact, it can be difficult to discern the additional detail differences between a 1080p unit and a 720p when viewing a screen size less than 50" (in the right viewing ranges).
There's more at the link, including recommendations, if you're interested.
RLC