This page will let you convert a large number of locations in various coordinate systems (such as latitude/longitude) to their approximate address or convert between coordinate systems. Paste them into the input box (latitude/longitude should be 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 box below should have the approximate addresses (converting between coordinate systems is much quicker). 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.