PhotoRec can recover your deleted photos from your digital camera or memory card.
All memory cards1 use the FAT32 file system from Microsoft. This filesystem does not physically delete files, but just marks them as deleted.
I needed to a tool to quickly let me recover or undelete all those photos. An “apt-cache search dos recovery” in Ubuntu yielded this beauty:
It contains a utility called PhotoRec which scans any device for any filetypes that you specify.
TestDisk also performs some more serious recovery functions, so bookmark it for a rainy day.
1 As far as I know?