I used to use pipex, and its fine until you want to talk to support - then its awful. One month I spent more on phone charges to Pipex then the monthly adsl charge was!
At the moment I'm using fast.co.uk who are most helpful. The one time I had to ring up support to change my CC details, the phone was answered in 2-3 rings. I've not had any reason to call them since, as I've had no noticeable downtime in over a year. I have a dedicated IP, and a web/mail/... server running from home with no problems
Jee