Digital Inspiration’s Find Postal Address … site is a one-trick pony, but does it well. Zoom to a location in Google Maps, click on the map, and a pop-up will give you the closest postal address to the point you’re clicking on:
A search box aids in zooming in quickly to a desired city or zip code.
Interesting note: This site in enslaved to Google Maps. I clicked on my house and received the correct street address, but the wrong town. This same mistake is made in Street View (I reported it almost a month ago).