The major problem with plasma, apart from still being uber-expensive compared to other options, is that if something goes wrong with the gas in them (and things do go wrong with the gas in them), they are done. Disposable TV. They can't be fixed.
LCD's have gotten a bit better, but they cannot display a true black and have motion artifacts to varying degrees on fast moving images (really not cool if you watch a lot of sports).
DLP technology has been around awhile and has the bugs worked out of it, and has already recouped it's R&D costs so the overall pricing of DLP units tends to run a bit cheaper. And, if the lamp in your DLP projection unit goes out or starts losing luminosity, you can put a new one in and you've got a brand new TV again. The downside is that they aren't available in a thin version that you can hang on your wall as they require a bit of depth in order for the projection to function properly. But, the picture is just amazing on them. I have a Samsung DLP HDTV that puts the picture on all the plasma and LCD TV's I have seen that have cost much more, including the one's some of my audiophile/videophile friends have, to shame.
Do some serious reading on all three technologies if you're in the market for one of these TV's. I'd steer away from plasma altogether. Too many issues can happen with those things and when a plasma unit dies, it's dead. LCD will work if you go high end to minimize motion artifacts and get a bit closer to true black, but that's only if you have a mad-on for hanging the thing on your wall for some reason. Otherwise, the picture on DLP's just can't be beat for the money in my opinion. Watch the prices this year on large flat-screen TV's. They're supposed to dip by $500 or more this summer sometime.
jag