Recommendation may not be the suitable word to use here...
There are very few unmetered ISPs open to you - I think on of your few (and strangely - best) options would be AOL. There are lots of opinions on them - some people find them good, whilst others no so...
Things to bear in mind whichever ISP you go for are:
Usage limits: yes, they're "unmetered" - but few ISPs offer unlimited usage for £15 pm - and those who do probably won't be around that long... with the exception of AOL who are pretty much unlimited for £16 pm).
User to Port contention ratio: Many ISPs don't publise this, but where possible you want to aim for at worst 10:1 contention ratio - hopefully better, depending on the usage limits imposed.
Basically, the lower the ratio (i.e. closer to 1:1) the more chance you have of connecting when you want rather than when you can...
The most important thing to remember is to read the terms and conditions fully - I know they're mostly boring dribble, but ISPs have a habbit of hiding things away so only to wise realise what they're getting into. Depending on your requirements, the terms can heavily influence your ISP choice (it's basically the usage limits you check for - most of the other stuff tends to be fairly standard... not spamming etc.).
Hope this helps you - want more info. on anything just ask!