Another recommendation here for Data Rescue.
I've also heard good things about "Stellar Phoenix Data Recovery" (probably works in a manner very similar to DR3), although I haven't tried it.
As you discovered, it can be risky to attempt a repartition without backing up the data on the drive first.
As one who has had to resort to Data Rescue to retrieve data from a damaged partition, I'd like to offer a few tips.
You may find that with the drive's partition info damaged, it may not be possible to get _any_ of the old partitions to mount on the desktop. The problem is that DR3 or Stellar Phoenix can't "reach" the damaged partitions, either, because the drives won't "mount up".
If this is the case, don't give up. There is a seemingly radical and dangerous "workaround" that _can_ work. In fact, it DID work for me when nothing else would.
That workaround is to use Disk Utility to completely RE-INITIALIZE the drive into a single, empty partition (yes, I mean what I wrote).
DO NOT "ZERO OUT" THE DRIVE (shouting intentional).
Just "intialize" it.
Yes, this WILL -destroy- all pre-existing partition info on the drive. This was EXACTLY my intent when I did it, because it was all-but impossible to "fix" the damaged partition information (and thus, to mount the drives).
But think for a moment -- when you re-initialize a drive, you aren't really doing much to the actual _data_ that resides on the drive sectors. All you're doing is wiping out the drive's directory -- the "index" that "points to" the data on the drives. The actual data remains "untouched", although there is no way for a normal file system to "see it", because the directory and pathways to that data don't exist any more.
But programs like DR3 and Stellar Phoenix are specifically designed to ignore the directories, and to "look" directly to the drive sectors. They "scavenge" the drives, saving whatever data they can find, and then attempt to reconstruct it afterwards.
(SIDE NOTE: You absolutely MUST HAVE a SECOND, blank drive to which you will recover the data. DR3 and Stellar Phoenix don't attempt to "repair" a bad drive -- they just try to scrounge whatever they can from it, and they need a second drive for the recovered files). You will not be able to use either of these programs in any effective way unless you buy a second external drive to serve as your recovery drive.
Can you see now why it was necessary to re-initialize the drive into a single partition? Once you do this, now you can "mount" the [seemingly empty] drive on the desktop. Once mounted, DR3 and Stellar Phoenix can "attack" it, even though there are no pathways to the old data -- because they don't need that. The recovery software can now "do its thing", and check every block of data on the drive, and put the results onto the "recovery drive".
It WILL take a LONG time for DR3 and SP to scan and scavenge the drives.
You WILL lose ALL your pre-existing folder hierarchies (remember, folder hierarchies are a construct of the old directories, which no longer exist).
But it CAN be done.
Again, this method worked for me when it looked like the old, corrupted partitions would never be "mountable" again.
