Another vote for TrueCrypt - http://www.truecrypt.org/

Very easy to use.

I met Phil Zimmerman, the originator of PGP at a training session almost 20 years ago. He was trying to persuade a group of us that he didn't feel guilty about providing software which allowed child pornographers to secure evidence and protect them from prosecution. Encryption is like most tools... it can be used for good or bad, depending on the intentions of the user.