Get one with 2 HDMI ports (for HD programming), and 1080p (the best picture quality available to the "regular" consumer right now).
Plasmas are generally cheaper for 42" and above, but LCD has come down alot in price over the past year. Both have their pros and cons. Most plasmas now are rated for something like 16,000-20,000 hours, so unless you watch tv 8 hours a day for 15-20 years, you won't have any problems. They will probably have "holographic tvs" by then
Plasmas are good for lower light rooms and have great "viewabilily" from all angles.
As for LCDs, their technology is a little newer for tvs, and the more common problem is the chance of pixels burning out (I've seen this on LCD computer monitors and the viewfinder on the back of digital cameras). LCDs are good for higher light rooms and aren't as good if you want to view from a sharp angle.
Pioneer has arguably the best plasmas but they're expensive. Sony Bravia XBR2 & XBR3 are nice higher end LCD tvs. Panasonic plasma I think is the best bang for your buck, but if you got the bucks then go for one of the above.