Need help with hard drive restore!

I did something really stupid and accidentally deleted the primary (and only) partition on a USB hard drive. What are my options for restoring the data? I have not reformatted it or done anything more to the drive other than delete the partition. Is there software that can reverse this?

There is a free and excellent tool to recover deleted partitions: TestDisk

I managed to get the partition restored last night. Sometimes I amaze myself at just how dumb I can be.