A mate of mine gets through tellies at a frightening rate (buys one, doesn't like it, sells it on and buys another). The best one I saw was a smaller (32"?) one that was apparently loads better quality than some of the others, yet cost more.
He sold that one too, so I can't tell you what it was. The worst was a huuuuge 50+" thing; just too 'pixelated' and fuzzy. I don't know why anyone wants one of those for the average sized living room. Think about the space the thing's going to be in, and how far away from it you'll be. I make do with a 28" monitor for DVDs and stuff; it's more than adequate for me.
Quality over quantity. Go to a place where you can sit as close to the equivalent position to your home, and try a few out.
Bear in mind something large can really dominate a space. You don't want some ugly behemoth sitting taking up loads of space when it's not in use.