Adobe Photoshop Express, Free!
Yes, I did just use “Photoshop” and “free” in the same sentence. It took me a while to get over the shock, but once I started using Adobe Photoshop Express, I was pleased with what I found. Obviously the express version is significantly pared down from its $700 computer counterpart, but this was the first (and so far only) app I’ve found that can do basic edits like cropping, straightening, adjusting exposure/saturation/tint/contrast, adding a monotone tint, and soft focus.
The main thing that sets Adobe Photoshop Express apart from other photo apps is that the user is completely in control. Other apps only give you pre-made effects–PS Express lets you decide whether to use the effects it comes with (which are OK but not spectacular) or make an image entirely your own. This is a program for the tinkerers–those who want to take control of every aspect of the image and perfect a basic image or come up with an effect that is different from the one everyone else has.
If I could only have one photo editing app on my iPhone, Adobe Photoshop Express would be it. Other apps give you limited options to choose from, PS Express gives you the ability to create your own.