If you play games, it seems like a very bad decision to buy Plasma, in my opinion. I would not spend over £1k on a screen that I could permanently damage just from playing games or watching the same channel for a while. (channel logos will also burn in)
Many plasma owners claim that they only suffer from "image retention" and not burn-in anymore, but this can last weeks, if not months, depending on the severity. (it took a friend about 3 months to completely get rid of "image retention" on his Sony plasma a while ago, after playing some games on it)
If blacks are a concern, and you only plan to use it as a television (no VGA connection for a PC) then the Sony BRAVIAs are the ones to go for. With the Power Saving mode on, and any kind of light in the room, blacks are better than I've seen on any display. They are very convincing, and it produces a great image. The problem with CRT/Plasma is that if there's any light on in the room, you get loads of reflections which makes the picture look crap.
In a fully dark room, CRT is capable of producing blacker blacks, but with the four CRTs we've got here, the LCD was darker when showing shadow detail. (if you make blacks truly black on all CRTs I've seen, you get no detail in the shadows at all)
I don't know how plasma compares, but I was very impressed with the black level of my Sony KDLV26A12U after three other LCDs that failed to impress in this regard.