In that price range you should have a lot to choose from. Obviously, you want a set that is at least HD-Ready and I'd suggest a 16:9 screen -- although that is a personal choice for you to make depending on your viewing habits.
I'd suggest taking a look at Toshiba, Mits, Pioneer and Sony. The Pioneer elites are probably my favorite RPTVs, but the are just to darn expensive. Both Toshiba and Mits make some great 65" sets and are the two biggest sellers in the U.S. You'll be happy with either, my only suggestion is that you only look at the 2001 lines. Things are changing fast and its not worth the little you will save by getting last year's model.
As for 4:3 sets -- just make sure you know what your getting. There is far too much misinformation on how many HD lines they can display on a 4:3 set. Some are truely capable of 1080 lines (not all truely defined though), while others only go to around 800. IMHO, Toshiba is the biggest offender in the 4:3 area and would not buy one (although I'd have no problem buying their 16:9 sets).
Find a few local dealers and go out and look at them. Just remember that they may not be set up the best and you may need to adjust contrast, brightness and color. Also, bring a few of your favorite DVDs to view.
My DVD List