The latest issue of Which? magazine includes a poll on the best ISPs (based on user recommendation).

The following came out above average.

clara.net (71%)
waitrose.com (61%)
plusnet (59%)
pipex (53%)
Demon (52%)
Blueyonder (50%)
One.tel (43%)

Bottom of the list were NTL, Wanadoo and supanet.

Not sure if all of the above provide broadband, but it at least gives you an idea.