free/open-source tools

• photorec — recover deleted files, via file carving
• testdisk — recover deleted partitions
• GNU ddrescue — like dd, but doesn't get hung up on bad sectors
• The Sleuth Kit
• fsck
  • fsck.vfat
  • fsck.ext3
  • etc...
• fatback — undeletes files from FAT partitions
• pre-emptive checking
  • smartctl -a /dev/sda — can be found on: Knoppix, ...
• great list at ForensicsWiki.org

articles

• Bad block HOWTO for smartmontools
• Recovering from file system corruption using TestDisk, Debian-Administration
• LOTS of stuff at cgsecurity.org