Excellent tool to recover lost photos, corrupted files from SD cards and such:

http://www.cgsecurity.org/wiki/PhotoRec

http://www.cgsecurity.org/wiki/PhotoRec_Step_By_Step

Other data recovery tools:

http://www.computerworld.com/s/article/9224577/6_data_recovery_tools_for_SD_cards_USB_drives_and_more?taxonomyId=150&pageNumber=1