As you might expect, we take a lot of screenshots here at TUAW, so I'm always interested in ways of making it easier. Most of the time I either use ImageWell or one of the built-in keyboard shortcuts. Nonetheless, InstantShot! looks like a convenient alternative for folks who prefer using the mouse. This little menubar utility waits quietly until you need to make a screenshot and is only a mouse-click away.
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.