It offers most of the same options as OS X's built-in Grab application, but is a bit more configurable as to file format. You can also use it to take multiple shots (like on a digital camera) every so many seconds (configurable in the Preferences). There's also an option to hide your desktop with a solid color, but it's not quite as nice-looking as Backdrop.
InstantShot! is Universal Binary and a free download from Digital Waters.