TrueCrypt has been around for a while on the Windows platform. I first learned about it when the great "Security Now" podcast <http://www.grc.com/securitynow.htm> devoted an entire episode to it. TrueCrypt is now available for OS X and there's a new GUI version for Linux. This is great! I use Truecrypt to encrypt the data on my many USB Flash Drives. I can now use these encrypted flash drives on all three platforms. TrueCrypt can encrypt entire volumes, partitions, or you can create an encrypted file (kind of like a disk image) onto which you can store your most important data.

There is so much that TrueCrypt does. I have only scratched the surface. Listen to the Security Now podcast on TrueCrypt. The TrueCrypt is extremely thorough, but needs to be completely updated for Mac and Linux.