(For rooted devices only!) DiskDigger can undelete and recover lost photos and images from your memory card or internal memory. Whether you accidentally deleted a photo, or even reformatted your memory card, DiskDigger's powerful data recovery features can find your lost pictures and let you restore them, or send them to an email account. For complete instructions, please see http://diskdigger.org/android
Again, this app is for rooted devices only! This is also a work-in-progress app (and not nearly as powerful as the original DiskDigger for Windows), so all constructive feedback and requests for features are welcome!
If you need to recover more types of files besides photos, try DiskDigger Pro!