Cooks Illustrated has the following tip:
For safety reasons, the U.S. Food and Drug Administration (FDA) recommends cooling liquids to 70 degrees within the first two hours after cooking and 40 degrees within four hours after that.
The easiest method was to put the hot pot of soup in the refrigerator. The boiling soup cooled from 212 degrees to 40 degrees in a total time of four hours and 15 minutes. However, the fridge's temperature rose to nearly 50 degrees, which is unsafe for everything else being stored in there. We found that by letting the soup cool to 85 degrees on the countertop (which took only an hour) before transferring it to the fridge, we could bring it down to 40 degrees in a total time of four hours and 30 minutes (well within the FDA's recommended range), and the fridge never got above 40 degrees.
This tip would seem to depend on the amount of soup you need to cool. I suppose if you've already portioned the soup into 3- to 5-cup bowls, the hour-long approximation for cooling soup to 85 degrees would be about right. However, we often leave a large stock pot of soup on the stove to cool, which would obviously take much longer to cool. All this to say, it'll take some experimentation to figure out the amount of time necessary to reach 85 degrees.