Pixlr Express from Autodesk is a photo editing application for the iOS and Android that lets you modify and edit your pictures and images quickly. This free app also has a complete set of tools for cropping, resizing, rotating and other image editing tasks that you may have in mind.
Aviary Photo Editor is no Photoshop, but it is one of the most powerful photo editors for the Android and iOS. Aside from being comprehensive, it is also easy to use. The app by Aviary Inc opens up to all your saved photos so you can easily go through your images and select the one you want to edit. You can also snap a new photo and import it into Aviary.