I recommend these guys: http://www.laptop-battery.org.uk/
They're based in Hong Kong and I would not normally have bought from them if they hadn't been recommended to me by a guy on a course I ran recently. He had a sony laptop, like me, and the battery had failed so he bought a new one. It has better battery life than the old one and it only cost £50.
Based on his recommendation I emailed them with my laptop details, they recommended a battery very quickly, I bought it, it arrived quickly, I've been using it fora couple of weeks and it's superb.
It cost £50. They're £300 new. This battery lasts much longer than the old one.
As a consequence: I've put my netbook away and I'm using my 2 year-old battered, but rejuvinated, laptop instead. The keyboard is bigger and now the battery is too.
I really dispise Sony, btw, for "gouging" me.