This free app from Microsoft allows you to create amazing panoramic photos with 360 degrees of lateral viewing and close to 360 degrees of vertical viewing. This is an amazing TED talk from one of the creators of this application. Using the iPhone camera, you take a series of pictures that are stitched together. Within the application and the Photosynth.net website, you can change the perspective of the view (see sample below). The application can also create flat panoramic images that can be used in other programs.
CamWow is a free iPhone app that simulates some of the effects available in PhotoBooth for Mac/iPad. The free version puts a CamWow watermark on the corner of any images captured in the tool (of course can be cropped out post-production). For $1.99 you can get the paid version which will take pictures without the watermark.
FatBooth is really just a bit of silliness. You can take a photo of someone and then the app will 'compute' what that person might look like having put on some extra weight. What I am most interested in is a feature I have not yet seen in other apps. When aligning certain markers with features on the photo (eyes, mouth) a finger would normally obscure the photo and thus make it difficult to be precise. In FatBooth, a zoom window appears above where your finger is placed and as a result you can align their markers with the photo with pretty good precision.
Header photo by Robert S. Donovan