Linux – Accidentally formated external usb harddrive (500GB) with bootable iso (1GB), how can I recover the data

I was attempting to create a bootable usb thumbdrive from the ubuntu install cd using UNetBootin. Unfortunately, I accidental wrote the live cd to my 500gb usb external drive (which was almost completely filled with important files). I noticed I had made this mistake almost as soon as it happened. I quickly unplugged the usb hard drive. Ubuntu is no longer able to mount the harddrive. I believe the disk was originally formated ntfs or ext3, but I forget.

I want to recover my data.

1. How can I determine the file-system type(ntfs or ext3) without mounting the disk?
2. Has anyone done this and recovered all or some of there data? How?
3. What /suggestions does server-fault have?
4. Can I recover in-place? That is do I need to find a >500GB harddrive onto which I can recover too?
5. Is there anyway to just recover the file system.
6. Can I see what files are intact?
7. Any favourite/best tools for recovery?

Thanks, and feel free to tell me that keeping backups is important (A backup NAS is in the main).

Note:

• I'm looking for free solutions
• I have read this earlier question 'how-do-you-repair-a-damaged-or-corrupt-partition', but I'm unsure if it applies completely to my case. As in my case I likely overwrote a fairly small amount of contiguous data at the beginning of the disk.
• As I was following verbatim the ubuntu directions on building a bootable usb drive, I'm assuming people have done exactly what I've done in the past, and I am interested in hearing how they solved it. Furthermore it is a case people are likely to run into in the future, so a set of clear directions on how to solve it would be extremely helpful for the community.