Check out
http://www.uswitch.com/broadband/best-broadban d/
That's a start
We've just switched from orange to O2, changed over last night the quality of the service for what you pay is brilliant, OK I know there is a run-in period bur even with the desktop and laptop running we were getting 7.96Mb on a speedtest. If you have an O2 mobile it's �7:34/month and just under �13 if not. If you are not within the catchment area they still may be able to suplly you but it's about �17 for an O2 mobile customer �22 if not.
HTH