The important things to consider are:
1. Contrast Ratio - the higher the better (10 000:1 is a MINIMUM these days).

and

2. Resolution - 1080p - a lot of TVs say they are High Def but sometimes they are referring to the tuner (it can pick up high def signals).

There's a lot of hype about HDTV and BlueRay today, but think before you invest lots more money in this - how often do you rent or buy one of the more expensive Blue Ray disks. I know I don't ever even think about buying them. Do you really need to see Angelina's pimples?