ioShutter is a cable which, when paired with an iOS app, becomes a remote shutter release controller for an SLR camera.
The app comes with a 20- or 60-second timer for delayed shots, a bulb mode with slow shutter speeds for night photography, and a time lapse mode. Other features include the ability to take pictures by making noise (yes, screaming or banging around will do the trick) and ShakeToTake mode, where you take a picture by shaking your iOS device.
There are different cables, depending on which camera you want to use. A lite app with limited functionality is free, but the full app costs $10.