TestDisk & PhotoRec: nice tools to recover lost partitions & files

TestDisk + PhotoRec is a nice toolset to recover lost disk partitions (or at least rescue some files from corrupted filesystems) in case of storage media failures, re-partitioning errors etc.
Works for disk images too.
More to say, it's a free & open source (GPL v2+) cross-platform (Linux, *BSD, Apple Mac OS X, Oracle / Sun Solaris, MS-DOS, MS Windows) software.

Presently, in Debian-based Linux distros, TestDisk & PhotoRec have been packaged into a single testdisk package, so you can install both tools at once:

# apt-get install testdisk