If you really want to go plasma, the best on the market was Pioneer’s Elite Kuro, nothing was within a generation of it, it was the best, may still be. But that was before Pioneer left the market and handed it over to Panasonic – I haven’t kept up with it to see how their handling it but there’s a model launching this year (called Viera I think), and it’s definitely worth a look. The other issue with plasma is burn in (yes, it happens on LCD’s too), I’m sure plenty of people would say oh it’s not a big deal, hardly an issue any more, that’s a bunch of BS once it happens (and I’ve seen it happen), if you’re going to drop that kind of cash on a TV think about your viewing habits before you do so. Leave it on a “ticker” channel all day, yeah, you and burn in are going to be friends.
For LCD, it’s all shifting to LED now, the difference is mainly how the LED’s are arranged. Samsung’s 8500 series was the best on the market last year (they’re now doing 9 series sets and they look beautiful), LG came fairly close though (and had a better viewing angle) and Sony’s Bravia got a lot of press too, I’ve heard some people rag on them but the couple I’ve seen consistently are pretty. In the end, there isn’t a whole lot that separates them, a lot comes down to how much of a videophile you are.
Keep in mind if you’re checking them out in the store all the levels are boosted to make the picture as clear and bright and contrasty as possible. Unless you want to be buying a new TV in a couple years you won’t be running it like that and unless you have a proper HT set up you won’t have room lighting like theirs either. You can take a demo quality blue ray that you know well (Planet Earth from BBC works pretty well for this) and have them pop it in and let you play around with the levels or have them adjust them down for you so it looks a little more realistic.
Don’t worry too much about OLED’s yet, they’re flat out gorgeous, but last I saw it’s going to be 2012 before the first 40+ sizes are released that don’t cost as much as a car, courtesy of LG.
Finally you’ll be looking at a lot of 3D tv’s coming out, if you want the latest and greatest, wait for your chosen line to release theirs if they haven’t already. If you don’t care about 3D (and I have to admit, I really don’t) you can probably cut a deal with them on the previous generations pricing.
Oh and for all that don’t forget to make sure you have a solid Blu-Ray player. Again Samsung and Sony (PS3 is actually still one of the best out there for the price) both make great boxes, you have to compare the options for yourself, I’m actually partial to Oppo myself. Though of course you could always go all out and get a Denon or Marantz flagship model. But then you might as well build and extention to your house specifically for your HT, why? Because you can!