www.freedom2surf.net
I pay £22.50 per month. It's a 512 connection. I could get faster for pretty much the same price (or it might be cheaper even) but that would involve a download/upload cap so I just stick with what I have.
The service is very good. When I first got connected I had a load of problems (due to me being a retard, there was nothing wrong with the connection itself) and they replied to all my e-mails quickly and informatively. I haven't needed to get in contact with them since cos my connection's been fine.