PGP 9.0 is the king pimp-daddy of them all. They publish the source code so you can trust that it doesn't have any back doors for the NSA/CIA/FBI/your mom. You can create SDA (self decrypting archives) that basically just zip up a bunch of files into an .exe file. Send that file to someone and when they click on the .exe, it asks for a password and then uncompresses. The only catch is that the person you're sending the file to has to know the password ahead of time and most email services won't let you send .exe files. If you have the other person's "public" key, then you can zip your files then encrypt it and send it to them without having to share a password first. Also has a file shredder. Also lets you wipe the free space on a hard drive. Also encrypts AIM instant messages. Also automatically encrypts emails sent to people you know (if you want to set it up that way). I've heard of a free program called "ccrypt" but haven't used it for anything yet. I think it's mostly for Unix computers though.