The most popular flatscreen technology is the LCD, or liquid crystal display. They're thinner than the rear-projection displays that are now extinct, and cheaper (on the whole) than the plasma screens that are nearing extinction. But in their ongoing quest to confuse customers, TV-makers have started calling newer LCD models LEDs (light-emitting diodes), because their screens are backlit with brighter, longer-lasting, and more energy-efficient LEDs. To make things even more disorienting, the past year or so has seen the release of a handful of OLED (organic LED) TVs, which are even more vibrant than LED screens.
Here's all you need to know: LED flatscreens are a legitimate, worthwhile step up from standard LCD TVs, with increased durability and better picture quality. Big screen OLEDs, however, are barely out of the lab, ludicrously expensive, and something you should think about in five to ten years.