Tripadvisor has always been a good resource for me. Good to check on attractions, see hotel ratings, etc.
If you're visiting the UK, pick up a GiffGaff sim card. Best deal around for data and voice. (you can pick one of these up on eBay before you travel to the UK:
http://www.ebay.co.uk/sch/i.html?_tr...at=0&_from=R40)