This happened yesterday to me. After a moment of fear, I started the searching the Net. I found lot of products, free and commercial, mainly for Windows.

I finally chose PhotoRec, because it is Open Source (GPL), multi-platform (I ran it on Ubuntu Linux), knows about CF cards (the kind of card used by my EOS 350D (Digital Rebel XT) and about Canon CR2 RAW format.

They claim it can work on formatted and damaged media also (but I hope I will never have to experiment).

It recovered all my shots.