Originally Posted by signupdamnit

Quit using the original drive immediately. Any subsequent writes to that drive reduce the probability of recovery!

Mount it as a slave (IOW, don't boot from it) and then use recovery utilities such as http://www.cgsecurity.org/wiki/PhotoRec (works for more than just photos) to at least be able to recover some of it. Whatever tool you use make sure not to try to recover the files to the same drive as this will harm the recovery efforts (any writes to the original disk can mean possible loss of the chance of recovery).

If the data means a lot to you and you can't understand these instructions or figure out the program well enough, I would disconnect the drive and call in a pro.

Sad to say but it looks like you rebooted and tried stuff like system recovery already. This probably means you will lose a lot of data. But the good news is that at least some of it should still be there.