I have recently moved to a new office and needed to post a letter during lunchtime. I have seen postboxes while on the way to the office but I wanted to find the nearest box so that I quickly pop out during the day and catch that days post.
So I turned to Google and found that Matthew Somerville has put together a site that combines Royal Mail's postbox location data, obtained under a freedom of information act request, with an interactive map. Bizarrely, Royal Mail does not actually know exactly where the postboxes are located. Matthew's site therefore relies on crowdsourcing to gain the location of many of the postboxes.
I think this is a useful resource and it only takes a minute to add the location of a box so why not type the post code of areas you know to see if you can help to complete it.