PHOTOREC is AWESOME.
Here's a How-To post from the Faceman Photography blog (your mileage may vary):
Here are the simple steps to running this under Mac OS X (FWIW, photos on the card were shot in Canon RAW and camera's CF card was mounted via a card reader under Mac OS X 10.4.9):
(1) Download PhotoRec v6.6 here. Don't worry that it's also a download for an app called TestDisk, which I haven't played with (yet).
(2) Uncompress the file testdisk-6.6.darwin.tar.bz2
(3) Inside the folder that results, you will find a folder called "darwin" that contains the UNIX executable called (unsurprisingly) "photorec".
(4) Double-click photorec to launch it into the terminal and here's what you'll see:
(5) Select the volume that represents your memory card and hit return to Proceed. In this case, /dev/disk1, is what we want.
(6) At the next screen, which looks like this:
select the partition table, which should be fine at the default setting of "Apple partition map" and hit return to get to this screen:
(7) "Search" will be highlighted. Hit return to start file recovery and you'll see this:
(8) "Other" should be highlighted and should work just fine (or at least it does for me with my setup). This will take you to the last step where you select what directory to recover to, in which case the default folder should be fine. Just select "Y" at this screen:
It will then start processing your memory card and saving what it finds to a folder called "recup_dir.1"
(9) Sit back or go make a sandwich and come back to a folder full of recovered files (hopefully)...
So, there it is. . . Your mileage may vary, but this is DEFINITELY handy to have for anyone who shoots with HDSLR's, or RED CF Cards. . .