I have a lot of camera apps but this is one of the most interesting, and is definitely a steal at todays fine price of nothing.
Slow Shutter Cam allows you to add some of the functionality of an SLR camera to your iPhone, without the gratuitous use of giant lenses.
You can choose from a range of shutter speeds, adjust, lock or set automatic exposure, set a countdown timer (great if you have a wee tripod) and change picture sizes.
With a bit of experimentation it is possible to achieve some amazing results. Night time shots in particular can produce awe inspiring photos that would look right at home in National Geographic.
This app is highly recommended and is just another step in the slow but steady march of your phone past your point and shoot and towards the lofty heights of a replacement for full featured DSLR.