I did a BUNCH of research before buying my TV.
Here were my basic findings:
Plasmas nice and thin, but if you plan to do a bunch of gaming, you do suffer the risk of image burn-in. Yes, the newer plasmas are getting better about it, but it still happens. And the plasmas that offer a white screen to remove burn in, keep in mind, while it works, it causes loss of lifespan to the TV. High cost is a factor is plasmas as well.
DLP technology is mostly good. Does not suffer image burn-in. The only downside I noticed with DLP is the processing time required to display an image. It's negligable for movies or TV, but when playing games (such as Halo 2), quick reactions are everything. I've seen some older sets that make games near unplayable, but again, newer ones tend to be quicker. Find a store with a DLP sitting next to an LCD (both displaying the same video) and you'll notice the image on the LCD changes before the DLP.
LCD doesn't have quite the contrast ratio as the other formats, but again doesn't suffer from image burn-in or the processing delay. Silicon LCD tends to be better with contrast, and also reduces the 'screen door' effect of LCD. But, Silicon LCD tends to be more expensive than DLP and a little cheaper than plasma.
I ended up buying the Sony SXRD (Silicon LCD).
I do a lot of gaming. I love the picture.
If I wasn't into gaming so much, I probably would have gone with a DLP. Great contrast, great picture, but I couldn't get over the picture delay.
But then again, DLP will be projection, so if you're looking sor something thin, Plasma or LCD is the way to go.
Good luck.