iExposure
If you’re new to shooting in PASM-mode, you probably are interested in getting the right manual values for your shutter-speed, aperture and so on and at the same time learn how these things work together.
With this app you will get a great introduction to all of that and also get som handy tips for different conditions. The app usually costs $1 but is now free.
Saarimner.com 
Wow, what a great tool. 🙂 Maybe I should get an IPhone afterall. Nah. 🙂 Thanks for sharing.
Haha.. 🙂
I sold my iPhone and am waiting to upgrade to a new one… missing it terribly 😦
Well it seems the new 4S is really awesome in terms of cpu-power and camera so I’ll guess you will be alright soon 😉