PGP, or more specifically OpenPGP is a great, and more importantly FREE method of securing your data and your e-mails. You don’t want “The Man” reading your e-mails, and neither do I.
There are many PGP and OpenPGP programs out there, but the one that is the most versatile that I have seen is called GnuPG. It comes in some form for every operating system. It comes standard with Ubuntu Linux, and there are versions for Windows and MAC.