FTK
If EnCase is the Microsoft Word of the digital evidence recovery world, then FTK (for Forensic Tool Kit) is the Macintosh. It's less popular, just in sheer numbers. But in a lot of ways, it's much easier to use, and some of the special functions, particularly when it comes to searching for, say, credit card numbers, buried on a hard drive, are much easier and faster.
Of course, EnCase is the big boy of the bunch, and I recommend first focusing your efforts here if you're new to forensics in general or digital evidence recovery in particular. But if you want to broaden your bases, and show potential employers how versatile you are, it's helpful to be able to say you know both.