A vectorized version of the St. John Ambulance logo exactly as it's seen on the outside of the 11th Doctor's TARDIS in my favorite television program, Doctor Who.
It's free to use, made in Adobe Illustrator CS5, but it should open in CS4 as well. Not sure about previous versions past that though.
(If any Doctor Who enthusiasts end up using it for their TARDIS reproductions be sure to leave me a link of your creation! I would love to see it)