Before you take a cutting torch to your own propane tank, make sure that it's complete empty of fuel. Or just leave the work up to Scott Krichau, who made this and other jack-o'-lanterns from empty tanks.
Link -via Dude Craft | Artist's Website | Photo: Skull-A-Day
UPDATE: In the comments, Jfhascall lets us know that these are actually refrigerant tanks. Much safer.