Due to a combination of circumstances (mostly self inflicted!) I lost a photo I'd just taken with my camera. I still had the SD card in the reader, but since I'd moved the photos off it to my hard disk, they'd all been deleted.

A quick hunt around found a program called photorec which would do the job. It could be installed under ubuntu using apt-get install testdisk and then started with photorec. It guided me through the disks on my machine to select the partition to recover from, and then asked where I wanted the recovered files saved in my home area. I then set it going and it found all the photos that had just been deleted, and many more besides! Excellent tool.