I and a few others here use Zen Internet, a bit more expensive than some but excellent reliability and customer service - use the search facility on this site and you'll find a few threads worth reading
Dont go with Orange! Their almost as bad as Tiscali!
Sorry to say Feckit but that Watchdog survey was not very good as it didn't include half of the ISP's out there.
Gizmo2006, check out DSLZone, for some customer ratings of the various ISP's out there.
FWIW, i'm with Vivaciti, an Entanet reseller, and the service is the best, I emailed support to get interleaving turned off they replied in less than 5 minutes, and it was done (by BT) the following day.
Do you know what services are available in your area? Or what kinda of speed your after? Check out Sam Knows for some insight on your lines capability. Any questions you know where to come.
Decided to go with a company called namesco via moneysupermarket (http://www.moneysupermarket.com/broadband/) They're only small but when I looked through their reviews people are saying fairly good things about them, with expections to one or two.
Got them coming round in a few weeks, so wish me luck! and I'll let you know how I get on.