This page will let you convert a large number of latitude/longitude pairs to their approximate address. Paste them into the left box (in the form Latitude,Longitude separated by either tabs or commas followed by new lines) and hit the 'Reverse geocode' button. Then go and make a cup of tea and when you return the right box should have the approximate addresses. Selecting Address components below will split the address into its parts (street name, postcode etc). Copy the output into a CSV file for easier manipulation.
Google throttles the number of requests that will be processed in a short period of time, so this page may appear to slow down, since it will retry failed requests after a short delay.
You results will appear below