free as in free speech vs free as in beer is my new favorite comparison.
That's actually a favorite way to explain open source. A few years back, some clever nerds came up with a microbrew beer recipe, which they then licensed as GNU/GPL open source (free as in speech), then they brewed and sold beer from this recipe at an open source expo.
And so, in nerd terms, this was hilarious: beer that was free as in free speech, but not free as in beer.