I haven't shopped in that range, so I can't really comment on specifics. It's hard to go wrong with a Sony.
My one piece of advice, regardless of size or TV type, is to ask to see it with a "regular" source - ie, a normal cable or satellite feed of a channel you watch regularly. Unless this is just for DVDs and HDTV, you will spend a lot of time with regular definition TV, and that is typically a place where the difference between a cheap TV and a more expensive TV shows up. They all look pretty darn good with a high-def source.
My one piece of advice, regardless of size or TV type, is to ask to see it with a "regular" source - ie, a normal cable or satellite feed of a channel you watch regularly. Unless this is just for DVDs and HDTV, you will spend a lot of time with regular definition TV, and that is typically a place where the difference between a cheap TV and a more expensive TV shows up. They all look pretty darn good with a high-def source.