OK....I have an uber-geek husband, so I will let you know what he says. =0) Here are the differences:
Plasma = Very heavy. Very expensive! Best contrast ratios (they show better "blacks") However, they will die after 4-8 years. This is due to the material inside. These tvs use a liquid that bounces electrons off of it creating the different colors. These liquids can't keep this up for more than the 4-8yr lifespan and it is impossible to replace, therefore, the tv is just useless and has to be thrown out. The "plasma" has already become old technology.
LCD = Very low weight. Not as expensive. Better investment over time. LCD tvs use a series of lamps inside, not the liquid that plasma tvs use. The lamps are completely replaceable, therefore extending the life of your TV.
Hubby says the one you want is an "LCD Array". This new technology uses a series of lamps creating a contrast comparable to the rockin' contrast of a new plasma, but still has the security of being replaceable after it's life is gone! =0)
.........Just the two cents of an uber-geek. Good luck with your decision! =0)