Panasonic 42" all the way - had mine (pre-HD) for about 2.5 years now, it's great - must admit I had sleepless nights worrying about how something the weight of my washing machine was going to hang above the fireplace!!!
On avforums.com there are a LOT of recommendations for
http://www.av-sales.co.uk/ - I wish I'd bought my plasma from them, I called them the day after I got my plasma (from Ebuyer.com on special) and ordered the wall mount, they got it to me the next day and they were very helpful over the phone, I won't hesitate to use them in the future.