Photoshop Mobile. Call it a bite-size version of the standard-setting photo editor. It’s not anywhere like the Photoshop we know but you can certainly crop, rotate, change color, soft focus, sketch and other one-touch effects.
Snapbox. It’s an all-in-one solution for the weekend warrior photographer with a wide range of photo filters and effects including Auto Correction, Lomograph, Noir, and Cinema. It also does not reduce the resolution of photos it processes like other apps.
Pop Art Lite. You want your 15 minutes, then by all means Warholize your iPhone pics with this nifty application. Does one thing and does it very well. An effortless way to have fun with your pics.
Flash For Free. Because the iPhone’s camera doesn’t have its own flash, this is perhaps the next best thing. Brighten your photos especially at nighttime with this simple but must-have app.
Crop For Free. From the makers of Flash For Free, also does one thing and does it very well. You can crop your photos multiple times without losing image quality.
And here's a review of Photoshop Mobile for iPhone: