resolution is how many pixels there are on the screen. the more pixels, the sharper and detailed the image will be. the HDTV standards are listed here:
http://en.wikipedia.org/wiki/High-definition_television#High-definition_display_resolutions
720p and 1080p are much preferable to 1080i.
plasma screens typically have far lower resolutions than LCDs, so careful with that. plasmas also can burn in, that is to say a static image that is being displayed for a long time (health bar in a game, for example) can "burn" into the screen and forever leave a shadow there. LCDs do not have that problem.
plasmas have better colour reproduction than LCDs, especially in dark greys and blacks.
pixel refresh rate is important in an LCD, the faster the better. too slow and the image looks like it's moving too slowly or "ghosty", so go for 5ms or faster.
contrast is good on virtually all brand name LCDs and especially plasmas, no problems there.
you will want at least two HDMI inputs, one for the console and another one for future HD content (satellite maybe), or for your PC.
if you want to hang it on your wall, make sure it is VESA mount compatible. most, but not all, large HDTVs are. "VESA mounts" is a standard mounting system.
i think that covers it... most importantly, try out the TV in-store using a fast-moving action film. try watching on your knees, looking up, and go from side to side to check that viewing angles are OK. make sure the LCD lamp has a 3 year warranty, not 1 year, they do burn out eventually. check the dead pixel policy (some manufacturers won't exchange an LCD unless you have at least 5 dead or stuck pixels).
and google up some reviews of models you are interested in.
