If you find yourself trying to remember what the wi-fi password was for an Apple Airport wi-fi access point (such as the Airport Extreme or Airport Express), and you remember/stored the base station password, then you’re in luck!

Start the Airport Utility.

Select the device for which you want to retrieve the password on the left.

Then, click Manual in the lower left corner:

And you’ll see a screen similar to this:

Then, from the application menu, select Base Station and Equivalent Network Password:

A dialog will be displayed:

At the top, your wi-fi password should be listed.

I copied it to 1Password so I wouldn’t lose the password again. :)