Just a quick post to mention I managed to get my data back of my external usb hard disk I thought I had lost. I downloaded an app called Partition Table Doctor from http://www.ptdd.com
As soon as I ran it, it found my external disk, and said it could repair the partition on it. It did its stuff, I saved the partition back to the disk rebooted and I could see the disk again.
It only cost $40, so its well worth it!