Macworld has published a relatively short article on computational photography, the broad name for combining information from several images into a single photograph (two examples are HDR imaging and panorama stitching). The article briefly discusses two free computational photography applications available for iOS devices.

One is Microsoft's Photosynth, which generates interactive 3D panorama images that you view with the free Photosynth.net service, or simple flat panoramas that can be viewed as normal photos. 

The other is called SynthCam, which makes still images from multiple iPhone video frames. By analyzing and combining the individual frames, SynthCam can create shallow depth of field images (otherwise impossible with a camera phone), reduce noise in high ISO shots, and create tilt-shift effects, albeit at video resolution.