remember, technology-wise, OLED is still young. however, plasma is about at its limit. plasma burns way too much energy, and the bulb burns out over time. it's unavoidable, but of course has been improved a lot. plasma has perfect black, and so does OLED. let me say that again for emphasis. OLED HAS PERFECT BLACK. Also, it's much more efficient energywise, so you're not increasing your carbon footprint. Check out power wattage ratings before you buy. my 52" LCD TV burns about 500W. And that's REALLY LOW compared to plasma TV's of the same size. OLED should be comparable or even less than the LCD.
technologywise:
plasma: electricity ionizes gas (creating plasma) that forms color on your screen. plasma traditionally has had less crispness for static images (ie: gaming, computer apps, etc) because of the gaseous nature of the pixels. however this has of course improved in recent times. it takes a lot of energy to ionize gas to the point that it lights up. this is also why they burn out. the blacks are true black because the electricity directly creates colored light. also, this requires some hefty glass to contain all that gas. plasma screens are REALLY HEAVY. http://en.wikipedia.org/wiki/Plasma_display
LCD: electricity alters the polarization of a liquid crystal layer behind a polarized screen. The screen is backlit by a bank of white LED's (usually). so black is not true black because you polarize the liquid crystal until it only mostly filters out all the white light from the backlight. however LED's are way more efficient than plasma. LCD TV's are not very heavy. just unwieldy at large sizes. more reading: http://en.wikipedia.org/wiki/Liquid_cry ... television http://en.wikipedia.org/wiki/Lcd
OLED ("LED"--not really an LED display): organic LED cells directly light up a pixel in the desired color. no backlight, no gases. electricity directly creates colored light in an efficient manner. the technology is relatively young, but this is really the best way to do this. I would wait a year or two and get an OLED TV, but my LCD TV is doing great, so I don't need another for a while. OLED TV's should not be very heavy either. more reading for you: http://en.wikipedia.org/wiki/Oled
Also, do a google search. Samsung is releasing a 6.9mm thick 50+" LCD TV later this year. that is so insanely cool.... plasma technology is spent. LCD is still improving. OLED is the way of the future.
note: a true LED TV is the type of thing you see on the side of a building in times square, tokyo, piccadilly, etc. 3 led's in a cluster per pixel. not really something someone mounts on their wall at home. it needs to be far enough away for your eyes to change the pixels into an image.
-Fong