Most of the time you head to Google Maps with an address in your head (or clipboard) with the goal of seeing it on a map. For those times when you're looking at a map and thinking "I wonder what the address is here," Google Maps has a handy shortcut for you.
Right-click the Google Map at any position you want the address and select "What's here?" Make sure you're zoomed in for accuracy (it can help to be in satellite view so you're sure you're clicking on the right spot). Google Maps will return the address of the location you clicked on, along with latitude and longitude.
Friend of Lifehacker and Digital Inspiration blogger Amit Agarwal created a webapp to tackle this duty a while back, but turns out this feature has been helpfully baked right into Google Maps if you know where to look.