plasma's only support a 720p at this time. the lcd supports a 1080P and new DLP's are starting to support 1080p but most are 1080i.
samsung is the only plasma so far that has 2 screen washer settings to help protect from screen burn. I have a 42 inch samsung plasma and without these features I would have been returning it already. The screen burn is rediculious.
I also bought a 56 inch toshiba DLP widescreen it only supports a 1080i, but most high def TV is broadcasted in 1080i so it if fine with the times. the real debate over 1080i/1080p is the war of high def dvd's. hd dvd vs. blu ray. hd dvd right now is 1080i the only thing right now in 1080p is the blu ray some things will be switching in the future. and for $1000 extra it can wait till you will use it on a more regular basis.
I would ask about screen burn protection, resolution,warrenty-protection plan, inputs (hdmi cables for best picture, and vga if you want to hook it up to your pc) choose something that is best quality with not so bad of a price. I really like the DLP more than than plasma, looking at lcd but too pricey.