Data Rescue II
And before you ask, no, there are no free utilities that will do this.
I would suggest turning off your machine, e.g. quit using it now. As in, even the cache for your browsing could be overwriting any files that you have deleted. Do not download anything to your internal drive, do not create new documents., etc.
edit:
Getting whatever it was off your backup would be the easiest way. And for the price of any of the data recovery utilities out there, you can get a good external drive.
Oh, and you should read the disclaimers on their site. They will be the about the same for any data recovery tool.