Make your own slide-on macro lens for the iPhone 4 or 4S. I designed this for my iPhone 4 when I couldn't find the image quality I wanted for less than $60.
Print this model and then buy the glass lens for $4 from Surplus Shed (http://www.surplusshed.com/). The Surplus Shed part number is L4471. For some reason the search box on the Surplus Shed home page does not work with part numbers. To get to L4471, use the "Lens Finder". In the Lens Finder type:
Lens Type: PCX, Plano Convex
Diameter: 12mm to 12mm
Focal length: 51mm to 51mm
It will get you to L4471
The lens fits in a recess in the model and is held in place with a few tiny drops of Superglue. If you get any glue on the lens it can cleaned off with nail polish remover or acetone. The lens is plano-convex (one side is flat). When inserted in the holder, the flat side of the lens faces the phone.
Note that the lens fits pretty snugly into the opening. Try fitting the lens before applying any glue. A good technique is, with the lens holder laying face-down on a table, lay the lens in position, and then push it into the recess by poking the lens with the eraser-end of a pencil. Once you know the lens fits cleanly, push it back out and put two tiny drops of superglue on opposite edges of the opening. I use a toothpick to apply the glue because squeezing the superglue directly out of the tube risks putting on too much. Then push the lens back in the same way as in the test fit.
The object pictures in the photo gallery (dime, ruler, and watch) are unedited and uncropped shots directly from my iPhone4.
This model will not slide over iPhone cases.