MarbleCam is another very popular app with iPhone photographers. MarbleCam takes pictures that look as if you had focused on a glass marble with a macro lens. The beautiful harmony of the scene appearing upside down within the marble and the blurred background make it look like you took your photo with a real marble or a soratama lens.
This app has just been updated with 25 new types of marble size and a small fix. This is a free update to a free app. You can download it here.