What is the best tool for recovering deleted data from a flash drive (pen drive)?
Fore Recovering data from external Hard drive
For Recovering files from internal and External hard drives there is PhotoRec that comes with TestDisk
Select the driver you have and inter on Proceed and follow the instruction. for help read the NOTE help on the footer.
The Ubuntu Wiki has an excellent page on Data recovery.
I've recently used the command line tool
(source: DataRecovery - Foremost)