md5deep is a suite of cross platform tools to compute hashes of any number of input files. Although similar to other hashing programs like md5sum, it can also recursively traverse directory structures, use a variety of algorithms, and use files of known hashes to perform both positive and negative matching. The program runs on Microsoft Windows, Apple OS X, Linux, Solaris, and most other *nix operating systems. It also also been ported to FreeBSD and is part of the Fink project.
md5deep homepage - http://md5deep.sourceforge.net/