TestDisk is powerful free data recovery software! It was primarily designed to help recover lost partitions and/or make non-booting disks bootable again when these symptoms are caused by faulty software, certain types of viruses or human error (such as accidentally deleting a Partition Table). Partition table recovery using TestDisk is really easy.
 
TestDisk can
Fix partition table, recover deleted partition
Recover FAT32 boot sector from its backup
Rebuild FAT12/FAT16/FAT32 boot sector
Fix FAT tables
Rebuild NTFS boot sector
Recover NTFS boot sector from its backup
Fix MFT using MFT mirror
Locate ext2/ext3/ext4 Backup SuperBlock
Undelete files from FAT, exFAT, NTFS and ext2 filesystem
Copy files from deleted FAT, exFAT, NTFS and ext2/ext3/ext4 partitions.

TestDisk has features for both novices and experts. For those who know little or nothing about data recovery techniques, TestDisk can be used to collect detailed information about a non-booting drive which can then be sent to a tech for further analysis. Those more familiar with such procedures should find TestDisk a handy tool in performing onsite recovery.
 
Operating systems

TestDisk can run under
DOS (either real or in a Windows 9x DOS-box),
Windows (NT4, 2000, XP, 2003, Vista, 2008, Windows 7 (x86 & x64),
Linux,
FreeBSD, NetBSD, OpenBSD,
SunOS and
MacOS X

Download: http://www.cgsecurity.org/wiki/TestDisk_Download binary executables and source files for DOS, Win32, MacOSX and Linux.

Documentation
TestDisk Step by Step to recover lost partitions and repair damaged FAT/NTFS boot sector
 TestDisk and Live rescue cd
TestDisk compilation. Developers are welcome to contribute code to TestDisk & PhotoRec.
 Recover deleted files Recover deleted files from NTFS partition
Undelete files and directories from FAT12, FAT16, FAT32 and exFAT filesystem. FAT file systems are commonly found on flash memory cards, digital cameras, and many other portable devices.
 Undelete files from ext2 filesystem

Recovery examples
Computer forensics self training using TestDisk & PhotoRec
Running the TestDisk Program , a menu by menu explanation
TestDisk FAQ
Support
TestDisk & PhotoRec In The News
TestDisk Team

To recover lost pictures or files from digital camera or harddisk, run the PhotoRec command.
 
Filesystems

TestDisk can find lost partitions for all of these file systems:
BeFS ( BeOS )
BSD disklabel ( FreeBSD/OpenBSD/NetBSD )
CramFS, Compressed File System
DOS/Windows FAT12, FAT16 and FAT32
Windows exFAT
HFS, HFS+ and HFSX, Hierarchical File System
JFS, IBM's Journaled File System
Linux btrfs
Linux ext2, ext3 and ext4
Linux LUKS encrypted partition
Linux RAID md 0.9/1.0/1.1/1.2 RAID 1: mirroring
RAID 4: striped array with parity device
RAID 5: striped array with distributed parity information
RAID 6: striped array with distributed dual redundancy information

Linux Swap (versions 1 and 2)
LVM and LVM2, Linux Logical Volume Manager
Mac partition map
Novell Storage Services NSS
NTFS ( Windows NT/2000/XP/2003/Vista/2008/7 )
ReiserFS 3.5, 3.6 and 4
Sun Solaris i386 disklabel
Unix File System UFS and UFS2 (Sun/BSD/...)
XFS, SGI's Journaled File System