123-reg.co.uk have been good; the service is okay too (email based) (for domains)
hostgator used to be cheap - about 4 dollars a month if you sign up for a few years and that comes with the domain name. I had a whole host of problems with their service when things DID go wrong (once in about 3 years) but they're pretty damn reliable.
was cheap; the place has been bought out. £36 for a year is pretty sweet though - I used to pay £80! - I don't know anything of the company that has bought them, so I can't vouch for them now, unfortunately.