You can make your own stamps at a few different sites (like this one) with pictures of your own choosing. So you could have firefly stamps! You can use an interesting icon or just a great shot. I don't know about the copyright issues but I am thinking they are won't be too stringent because you wouldn't be selling them and may even be art of your own making if you use an icon.
Anywho, corny - I know - but I thought I would share the idea. I am certainly having fun thinking of all the different ones I can make for people.