I currently use UK Web Hosting - UK Reseller Hosting - UK Managed Dedicated Servers - UK Domain Registration Services - their support team are absolutely brilliant, they have a great spam filtering system and they make backups of their servers 4 times a day :) .
The price is a little steep, but it's worth it for what you get.
You can purchase shared, reseller or dedicated plans.

However, recently I've been wanting to use custom programs such as subversion (Unfortunately UH do not support / allow you to install svn unless you own a dedicated server). Slicehost - VPS Hosting are supposed to be an excellent vps host, and I have not heard a single complaint about their servers / support.

Alex