md5deep is a cross-platform set of programs to compute MD5, SHA-1, SHA-256, Tiger, or Whirlpool message digests on an arbitrary number of files.

md5deep is similar to the md5sum program found in the GNU Coreutils package, but has additional features of recursive operation, comparison mode, piecewise and file type mode.

Basically if you want to know if that download you just spent 5 hours on is intact and not corrupt, this is the program for you.