I heart my iPhone, and the built-in camera is pretty decent for little snaps, but at times I get the hankering to change the exposure a bit for fancy pants effect or just to lighten things up. Alas, there is no control for the exposure on the iPhone and it usually under-exposes backlit scenes. So here's a trick I discovered. I call it Finger Priority Auto-Exposure.
Compose your shot then slide your extra finger partially over the lens. You'll see the scene brighten up as the auto-exposure tries to compensate. When it looks about right, snap the photo and as soon as you hear the shutter click, remove your finger. Since there is a slight delay between the snap sound and the actual capture, your finger is out of the photo but the auto-exposure hasn't had time to re-adjust yet and you have a brighter photo! It might take a few tries to get the timing and brightness just right, but it works! Check it out: