Originally Posted by MightyBobo

Before he answers that, I'll preface with this: getting files back is completely dependent on how long its been since you "deleted" the file. If its been a while, more than likely the file space where the file was existing was overwritten and wont be able to be recovered, barring some fancy schmancy expensive government equipment potentially. Same goes for formatting, but with formatting since you are destroying the original file system (UNLESS you did a "quick format"), you'd only be able to find chunks of your files if they are large. Smaller files would be pretty easy to find more than likely.

Think of your file system as a pointer to not only where files are, but where the rest of the file is. Most people don't realize that files aren't actually stored in one tidy spot on your hard drive - more often than not, they are scattered all over the thing in random open places called clusters (on windows machines). When you delete a file, its not actually deleted - the file system simply flags those clusters as being able to be overwritten with new data when it becomes available. This is why, during a criminal investigation, getting a hard drive intact without contaminating it is absolutely vital - overwriting the data the criminal tried to hide could be a case-breaker.

As far as SPECIFIC software, I dont know off hand other than some called EnCase, but an encase license tends to be very expensive. But if you have it, you can make it back easily, restoring data for people (hence why its very expensive...)