If you haven't made your purchase yet, I've been doing some research lately on gaming HDTVs as well. The Panasonic G10 series seems to be the best for gaming as far as input lag and response times go. The problem, though, is that even current plasma technologies still experience image retention and burn in if you aren't very careful. Playing games that have static HUDs for several hours at a time will definitely cause noticeable image retention (FPS's, fighting games that have health bars, etc). The black level will also fade the more you use the screen (after a few hundred hours). Personally, my play sessions are too long to consider a plasma.
You probably can not find a good quality 50 inch LCD for $1000 or under. After a few long research sessions, I'm looking towards the Sharp LC-46D65U for gaming. It's 46 inch, $1000, and most importantly, has very low input lag compared to other large LCDs. The main drawbacks I've read about are less than stellar black levels associated with the anti-glare coating and fading blacks when looking from an angle. This does not bother me, though, since the primary (80%) use of the screen would be for gaming.
Also, if gaming is your priority, stay away from Samsung models as they all have very high input lag (including their non-TN PC monitors).
There are so many TVs and so much info on all of them that buying a TV has become pretty tough these days unless you're the type of person that just walks into Best Buy and picks one. My best recommendation, of course, is to do tons of research and make an informed decision of your own.