Here is a "green" closing gift idea

Compact florescent light bulbs!  Save money, save energy, reduce your carbon footprint.  Go to http://www.18seconds.org/ for more information and to check and see how green your state is.  Don't let the look of that light bulb put you off.  There are now soft white CFL bulbs that look like regular spotlights and don't have that awful cold, blue look of a regular florescent. They are more expensive initially, but save lots of money over time.  When selecting your bulbs, compare the lumens with that of the incandesent bulb you normally buy, and then bump it up a little, and you will get just the right amount of light.  Give a couple to your clients as part of your closing gift and introduce them to the concept.