I did a guest post some time ago about some different iPhone apps I use for photography. This is kind of an update to that post, so to see more apps, please check out that post as well.
Anyone who knows me, knows I like to take photos...of everything...using anything. My iPhone 4S is with me at all times and it has a pretty decent camera. Believe it or not I have three go-to apps that I use to edit photos on my iPhone.
This app has over 100 effects, textures and frames. You can layer as many effects as you like using the "Add another" function.
A very strong app for editing. You can add filters, frames and do across the board tuning. However, the best part is the selective tuning (ie: dodging and burning) and detail tuning (ie: sharpening and structure).
This app offers lots of scenes, filter effects and borders. It also has nice rotate and cropping capabilities.
Other apps that I use from time to time for fun effects --
Takes pictures that look as if you had focused on a glass marble with a macro lens.
Converts a photo to a beautiful artistic rendering employing a creative interactive process.
There are many many iPhone photography apps out there, so I'm sure there will be another update to this list in the future.