Ever had the horror of accidentally erasing the photos from a memory card before they were saved? Or did you think they were saved only to have them be lost from your computer - and the disk has been erased? Even if you've started overwriting the erased disk with new photos, many of the images that used to be there can be recovered. I've used a couple of different programs for recovering photos from disks, and am happy to recommend a free program: Art Plus Photo Recovery 3.0. Free! Download the executable file (photorec.exe) and launch it to immediately begin your recovery. Connect the camera card to a reader, select the reader, select a folder to place recovered images, and then let the program run. In a few minutes, you'll be surprised to see most or all of your "erased" photos have been recovered. Erasing usually just deletes directory information on the card but does not remove the data that was there. Reformatting the card may do that - so just erase unless you have some kind of problem that requires reformatting, or unless you want to prevent others from recovering the images you had. (Spies take note - but even reformatting a memory card may not defeat high-tech recovery methods.)
I've also used Recover My Photos and thought it was pretty good and perhaps more thorough in recovering all kinds of files and file fragments (including movies - something that the Art Plus product may not recover), but it's $40. The free competitor might be adequate for most needs, so start there. And once you've recovered your photos, back them up so you don't have another tragedy.