On a recent trip to the US I bought myself an Olloclip, a tiny set of lenses designed to be used with the iPhone 4 and 4S.
The Olloclip, like its name suggests, is a quick-connect lens system which clips over the iPhone’s rear-facing camera, allowing you to take wide-angle, macro, and fisheye shots.
It comes with its own microfibre pouch for cleaning and safe keeping.
Check out the Olloclip website for prices and purchasing info.
[Disclaimer: I’ve not received a cent from either Olloclip or Apple for this post.]