Recover deleted files using Foremost

Foremost is a console program to recover files based on their headers, footers, and internal data structures. This process is commonly referred to as data carving. Foremost can work on image files, such as those generated by dd, Safeback, Encase, etc, or directly on a drive. The headers and footers can be specified by a configuration file or you can use command line switches to specify built-in file types. These built-in types look at the data structures of a given file format allowing for a more reliable and faster recovery.

Originally developed by the United States Air Force Office of Special Investigations and The Center for Information Systems Security Studies and Research and now foremost has been opened to the general public.

Files types supported by foremost:
jpg, gif, png, bmp
avi, mpg, wav, wmv, mov
pdf, doc, zip, exe, rff, rar, html, cpp

You can tweak /etc/foremost.conf to add support for more file types.
Please note that there's no guarantee that foremost will succeed in recovering your files, but at least there's a chance.

Foremost Installation:
Open the terminal and type following command to install foremost:

apt-get install foremost

Foremost isn’t the greatest solution; it recovers every file it sees and doesn’t support very many file types. It is possible to add types to the /etc/foremost.conf file, but it doesn’t look an easy task. However, if you’ve lost a bunch of photos or documents, Foremost could be just what you need.

Using Foremost:
Suppose you want to recover png file, from command line type following commad:

foremost -t png -i /dev/sda1

After completion, you will find a folder called output in the directory from where you executed the foremost, where within you can see the folder 'png' and inside png you can find your lost png file.

There are many more tools that you can use to recover your files:

Recover deleted files from NTFS filesystem from Ubuntu Linux - Ntfsundelete
Recover your deleted jpeg pictures from filesystem or camera memory card - recoverjpeg
Utility to recover deleted files from an ext3 or ext4 Linux partition - Extundelete
How to recover deleted pictures and Video files