Linux Distros Specifically For Data Recovery
A recovery-specific Linux distribution is the simplest place to start if you have a big recovery job ahead of you. You get a great many tools in one place, along with at least some degree of organization for them.
Many "tiny" distributions like Puppy Linux or DSL (two of my personal favorites) work nicely for this sort of thing, and are fine for just mounting a volume and copying files out by hand without doing anything special. That said, the technically savvy may be better off with a distro that has as many recovery-specific tools as possible built in.
The Gentoo-based SystemRescueCD distribution, for instance, packs a broad gamut of tools into a single 200-MB .ISO file. Boot it from a CD or USB drive and you can perform recovery functions either from a command line or an optional X desktop. SRCD does require some foreknowledge of Linux, though; if you're not comfortable doing things like manually mounting volumes from the command line, you might find yourself somewhat at sea. That said, it's possible to accomplish just about anything if you don't mind a bit of a learning curve.
Another recovery distribution that's a touch more user-friendly is Partedmagic. It features many of the same tools, but boots directly into an X desktop and provides graphical user interface access to some of the most common and powerful programs. Again, at least some knowledge of Linux is helpful, even if it's only basic techniques such as mounting or unmounting file systems, but less sophisticated users can probably start here.
Helix offers a markedly different interface than BackTrack or STD.
|(click for image gallery)|
Both distributions also give you the freedom to run the whole gamut of Linux applications out there, connect to the Internet if needed, and do most anything else that you might care to do. (They don't come with as broad a range of programs as most desktop distros, but, if you're so inclined, it's not hard to add applications of your choice or perform other customizations on the disk image.)
Experts who aren't daunted by the command line and want to get the full range of tools available can go for one of various live CD distributions compiled for performing forensic investigations of various kinds (with data recovery being one of several possible functions).
Another Knoppix re-spin for forensic / recovery work is Helix, which by default runs in what could be called "paranoid mode": it will not mount any file systems unless specifically commanded to do so. Since each one of these is a live CD, give each one a try and see which one you're most comfortable with out of the box.