I've been successull with "FileSalvage 6.0". I accidently deleted some stuff on my Firewire drive and wondered for a week where all that empty space came from... I used that external drive during that time, not knowing I had deleted something. If the drive to recover is not your system drive (where stuff gets written to when your RAM is full), chances are good that you can salvage it.
I could recover everything, only the filenames were gone. Spotlight helped though.