Here's something fun I thought I might share.
Many years ago, I disassembled a couple of Epson flatbed scanners to convert them to "light tables". In the process, I removed the innards and discovered that there was a cool little lens the Epsons use to capture a scanned document's image. It's called a "final Focus" lens and it's not all that large, and from I've been able to learn, about a focal length of 15mm (don't quote me on this). The end result, is that these things are awesome for using as a magnifying lens AND better still, makes an iPhone darn-near a microscope! Trying to hold the lens in place for a photo is almost like cat juggling, but the results are really cool!
I'll post some examples...all of the photos were taken with my iPhone 4S, by the way.
Here's a coule of shots with the lens next to a penny for scale.
Here's a macro of the penny using the iPhone's zoom
And here's the penny seen with the lens held up to the iPhone's lens
Here's a Motorola power transistor (close to an inch wide) using the iPhone's zoom
And here's the transistor seen with the lens held up to the iPhone's lens
And now for a completely random shot:
the tip of an inkpen seen through the lens held up to the iPhone's lens