There is a ton of photography apps out there for the iPhone. But the best overall photography is Camera+. It is the ultimate photography app and can help you get the most out of your iPhone camera.
It's a feature packed app, stuffing many different photography tweaks which make most other editing apps obsolete.
Touch exposure and focus - usually when focusing on something, the point of exposure is the same. With this feature you can choose where you want to focus but have the exposure point in a whole different place.
Shooting modes - you get a stabilizer feature which will only take the shot when the phone is super steady so you get a crisp image. You also get the common features such as timer and burst fire.
Clarity - with this feature you can brighten up your images where they are too dark. It works great on pictures taken with the iPhone camera.
Lightbox - the app comes with its very own lightbox, within which you can quickly view, edit and delete images.
Photo info - this amazing feature shows all the complex detailed info behind your picture. It shows info such as ISO, aperture, shutter speed, scene, effect, border and location data.
Sharing - a common feature which most photography apps have which lets you share to social networks.
FX - when editing you get a ton of editing options and effects which you can put over your picture. You can also change the intensity of these effects so you get it just right.
As on overall camera app, this is the best you can get for the iPhone. It's my main camera app and I have it in placed in the dock on my iPhone so I have quick access.
It's only £1.49 ($1.99) which is very reasonable compared to other photography apps and well worth the money.