The answer depends on several factors, especially the time of day you want to connect. Try the website http://www.08whatever.com
- use their excellent 'Unmetered ISP Wizard' to find an ISP that fits your requirements.
Have a look at
www.net4nowt.com
there you may find something tailored to your needs - the site lists allsorts of free ISPs and includes reviews - good & bad - by ordinary people that have actually used them.
By all accounts NTL is pretty good at the moment - they are charging �15 a month for 24hr 7 day a week access and you also get �15 worth of voice phone calls for your money as well.