Here is my choice and rankings:
1. 50PZ800
2. PN50A650
3. LN52A650
4. 52XBR4
Keep in mind, that all of these displays will present a wonderful picture. These are just choices and not favorites. All have strengths and weaknesses. If you have a brightly lit room LCDs would be ranked in higher priority. If you have controlled lighting the plasma should take top honors. Also if you throw the XBR4 it would only be fair to throw in the Pioneer 5020FD. That would be my choice over all of these displays.
Chris