First, you might want to make a backup for the SD card using USB image tool. (http://www.alexpage.de/usb-image-tool/)
After that, this methods might help you,
PhotoRec might help you. (http://www.cgsecurity.org/wiki/PhotoRec_Step_By_Step)
You might want to check out ZAR if that doesn't work. (http://www.z-a-recovery.com/)
If all else fails, you can quick format it and use a tool like Recuva to try and recover the data. You don't need to worry about formatting it as you already have a backup img from usb image tool which can be restored to the card.