Don't you have a backup of that data? Then you'll lose it sooner or later, so why care that you lost it now?
Anyway, in http://forums.cnet.com/7723-7588_102-354911/lost-and-found-or-the-storage-forum-sticky/ you'll read suggestions for recovery software. And you'll be able to find more if you google something like WINDOWS UNDELETE or WINDOWS UNFORMAT.
Be sure not to pay for software until you're sure it works for you.
Looks like I accidentally ran HP USB Disk Storage Format Tool on my 500gb Seagate External harddrive, and all my files are gone.
My computer is now prompting me to format the drive before it is useable.
Do you guys have any idea how I can retrieve these files back?