AVS is a great resource, but you have to have some general decisions already made before you go there, or you will be even more confused than when you started. You have your budget and screen size finished, but you still have to decide on plasma or lcd. The 2 sides bicker over there back and forth about which format is better. If you are undecided, none of the bickering will help you decide.
In general, plasma has better blacks and color, but tend to run a bit hot, can sometimes buzz and is susceptible to burn in. You have pretty limited options for plasma. Not many brands still carry them. I think the only brand out there for your budget is the Panasonic Viera.
LCD's have a ton of options for you. Maybe too many. A pretty good rule of thumb, for me anyway, is you pretty much can't go wrong if you stick with Samsung, Sony Bravia or even LG. Obviously stay away from the no name brands like insignia and walmart's flavor of the month. Vizio is a tough call. Some people love'em, some hate'em. I personally was leaning toward them, but found a great deal(at the time) on a Sony.
If you do go with LCD, you will also have to decide on refresh rates. 60, 120 or 240hz. Basically these are motion enhancements meant to smooth fast action content. Opinions on them also vary widely. I tend to dislike them, they seem a bit phony. Other people love them. Google "soap opera effect" to read up on the subject and decide for yourself.
Use the internet and AVS to narrow down your choices to a few specific models. Take those models and try to find a local Best Buy, Costco or BJ's B&M store that has as many of them on display as possible and see for yourself which one you like better. Let that be your deciding factor. Good luck.
i did a lot of research on those exact sizes about 7 months ago, and settled on the samsung LN40A650. It was between that and the Sony 40" W Series. For me, those two models, both with 120Hz, were leaps better than any other sets in that range. If you look around, you'll find both near $1000, and there are $899 deals every now and then if you don't mind waiting for it to pop up.