As mentioned in the above post Samsung plasmas seem to be unspoken of, they've never really stood out to me when walking around but I have heard good things, although good things are generally spoken of the higher spec models, not the 42" 4 series (although I have still heard good). I haven't read anything about the new ones either. Panasonic and LG will be your choices and if you want to look at Samsungs then do do.
Basically you have 2 options, the Panasonic P42X10 and the LG 42PQ6000, both £600 at Richer Sounds. I personally prefer the LG picture slightly but there is very little in it, the Panasonic is more resistant to image retention, but you don't need to worry about anything bad happening unless you spend 3 hours or more gaming at one time I would say. I have a PX80 and PG6000 (last years equivalent of the X10 and PQ6000) and there isn't much between them apart from the Panasonic has better black levels, but that's changed this year and they're very similar.
The credits rolling is a wierd area, it's phosphor lag on the plasma TVs, Panasonics are the worst for it among the decent brands but it only occasionally comes up on my PX80, it seems to come up at a certain speed of credits, so you see it some times and don't at others. My LG is better in this respect though, it comes up less often and to a lesser degree when it does come up.
Basically, if you want the best SD performance you can get for the money it's either those two TVs, I haven't seen an LCD which can compete in the same price range, you'll need to spend a lot more for SD TV quality on LCD in my opinion. But, believe it or not the Sony CRT might be better for SD content, depending on preference and the quality of the CRT itself...you wont regret the change when you get something in HD though!