The AVS Forum has a wealth of info on Plasmas/LCDs and other rear screen types such as DLP as well as projectors. I have been researching for about a year there, and it is very useful/helpful forum.
http://www.avsforum.com/avs-vb/As to which is best, it depends a lot on what you are doing and your personal preference. After lots of dithering, I am going for a Panasonic Plasma, they have very good blacks (better than most LCDs IMO). However, Pioneer, Fujitsu, and Hitachi plasmas tend to be very good, as well. I was also impressed with my brother-in-laws new DLP projector which are much cheaper than plasma and give you a very large picture (more of a movie like size). But to my eyes, plasmas still have the best picture. Plus, I can see the "infamous" rainbow effect on DLP types. Direct display LCDS are more expensive than plasmas at the larger sizes and are not available bigger than plus 37 inch (at least not without a load of gold). Bad thing about plasmas is they are expensive (42 inch Panisonic 1024x768 runs around $4K via reputable online vendors) and you have more concern with burn in, which is not an issue with DLP and LCDs. If you are going to keep a static image for long periods then plasma is not your choice (just like the older CRT rear projection TVs. As far as lifespan, plasmas have come a long way and most are running around 30,000 hours to half-brightness (CRT brightness degrades over time too). They also run cooler and have better fans. The ones I have looked at rarely can be heard from normal viewing distances. If you live at high altitudes (Denver), plasmas are not for you either, unless you like to hear buzzing. Oh, and there is no such thing as "refilling a plasma" tv, contrary to what some Best Buy sales types will tell you (as they pitch their extended warranty).
As with all things, your eyes should be the judge. However, you do have to watch out for the fact that many setups at places like Sears, Best Buy, CompUSA are horrible and very rarely do justice to any of the above type displays. If you can, compare from the same feeds, and with a quality input. Plus, garbage signal in...means really bad viewing on a big screen. What you would not have noticed on a 27" TV may be unwatchable with a 37" or bigger. If you have Dish TV or digital cable, you soon realize how much they compress the signals which tends to make things look like junk. But, my read on the general consensus is most of the above technologies look great with HDTV. SDTV can look really bad depending on your equipment, and type of signal.