Along with
www.adsl.com could I recommend
www.uswitch.com.
Things to look out for are:- monthly download limits. Some are restrictive but may suit you. Also check and compare the initial cost of setting up. The one's that appear cheap at face value may actually have an exorbitant initial setup cost. Go for the ones that are offering a competitive monthly charge with a low set up cost as within a year monthly charges are likely to have dropped.
Based on the above I chose Pipex on PPRuNers recommendations.
Hope this helps.