I haven’t tested it, but I have read that PhotoRescue Wizard is a great piece of software that really works. It can help you rescue deleted photos from your memory card. It can even help if the memory card was formatted! In the review where I read about the program they have stated that it rescued the photos that were deleted two times (delete and format, I guess).

The program is shareware that can be bought for US$29. There is a demo version that previews the rescued images so you can see if it works for you or not before buying it.