Recuva is one of the best free data recovery tools out there, and it is my personal favorite that I always recommend over similar file recovery programs. It is easy to use and is just as effective as any other freeware or premium file recovery program on the market. It is developed by Piriform, the makers of CCleaner, another excellent product.
I have been using Recuva almost exclusively over competitor products for a number of years now and have little to complain about.
To get started, visit the Recuva download page to get the software. The best option for someone who already has files to recover is the portable download (available here, hosted on Softonic). This will save you from having to install anything after you discover that you need to recover a file. If you are downloading the program for future use and have no files to recover, the standard installable download is fine.
A file recovery program can only recover a file that has been deleted from your computer if the same space on the hard drive has not been used by another file. Every time something is saved or installed, the chances of your file being recovered decrease. Using the portable version of Recuva prevents anything from being overwritten during installation.