If you get a 42" plasma, the native resolution is 1024x768, which is not true HD. The resolution for 720p is 1,280x720. Most people can't tell the difference, but just food for thought. In order to get 720p out of a plasma, you have to go 50" which is considerably more expensive. LCDs typically have a higher native resolution, but narrow viewing angles.
Personally, I think that the best bang for your buck is plasma when compared to LCD if you are getting a big set. The best plasma displays (Panasonic) have excellent pictures that rival CRT.
CNET has a dummy's guide to HDTVs:
http://www.cnet.com/4520-7874_1-5102...html?tag=prmo1
And this forum has a lot of helpful information:
http://www.highdefforum.com/