720p limits you to a maximum screen resolution of 1280x720, a 1080p enabled TV has a maximum resolution of 1920x1080.
Defiantly keep a close eye on contrast ratios, the higher the ratio the better the colour depth. My plasma has a contrast ratio of 33,000:1 where as some of the other TV's I looked had for the same money only had say 10,000:1.
I currently have a Sony Bravia KDL40V4000 and IMO it was by far the best TV out there for the money when I bought it £595 form Curry's.
Big-Dan.