A recent posting over at s/v Estrellita got me looking for boat stamps, and look at what I found:
A place where you can make your own custom postage! (Sorry for you non USians, it looks like it will only generate US postage). How cool is that!
The postage costs about twice what it does in the Post Office ($18.95 for a sheet of 20), so these are probably not what you'd use to pay your bills.