Tool for recovering deleted data from a flash drive

1. TestDisk

find lost partitions and data for External and Internal Drive for all of these file systems, ext2, ext3, ext4 and encrypted partition. for windows FAT12/FAT16/FAT32 and NTFS boot sector.

For Recovering data from external Hard drive
Type testdisk on your terminal and follow this well written step TestDisk Step-By-Step

For Recovering files from internal and External hard drives there is PhotoRec which comes with TestDisk.

type photorec on your terminal

Select your drive and hit enter to proceed and follow the instruction.

2. Extundelete

   extundelete is a utility that can recover deleted files from an ext3 or ext4 partition

The Ubuntu Wiki has an excellent page on Data recovery.

I've recently used the command line tool foremost for recovering 9000 photos off a SD card.

1. Install foremost: sudo apt-get install foremost
2. Mount and create the target directory for storing recovered data, make sure it's large enough to hold the data. I assume it's located at /media/backup/recover now.

3. Assuming your flash drive to be named /dev/sdb, run:

   sudo foremost -i /dev/sdb -o /media/backup/recover
   

4. Do something else, it might take a while to read and recover the data over USB.

(source: DataRecovery - Foremost)