Formatting doesn't actually delete any data it just removes the headers and the partition table etc. The data is still physically on the disk but there but there is no reference to it's location so your computer can't read it and you can't see it. The data is not truly gone until something is written over the top of it, sometimes it takes several overwrites.
If you haven't done anything since formatting there is a high chance one of the programs suggested above can recover it. You will need to connect the drive to another machine either as a secondary drive or via an external HDD enclosure and run the software from there.
Or alternatively you could create a bootable CD of PartedMagic and recover from there.