Great use for an empty growler

An empty growler, you say?  I know, it's a horrifying thought, but they do go empty from time to time.  In fact, if you're like me, the sheer number of growlers you own makes having them all filled at the same time nearly impossible.  Reading an article in the newest issue of Beer Magazine, I learned of a great use for the spare growlers you have sitting around.  Use them to ferment small batches of homebrew!  The size is perfect for small, experimental batches that you may not want a full 5 gallons of.  All you need is a #6 stopper and an airlock.  This is one of the best pieces of homebrew advice I have gotten in a long time, and I can't wait to put some of my dormant growlers to use.  Now, what to brew?