How to protect data from scumbag thieves?

Ok so I have a mac and a couple external drives. If they get stolen, how can I prevent the scumbags from accessing all my data? I don't care if my equipment is stolen, all I really care about is the data. I think I have to encrypt it or something, but I am not too sure. I know file vault is built into Leopard, and that protects my home folder. But what about my external drive data? How do I encrypt that, does anyone have any advice to protect data against scumbag theft?

truecrypt is your friend.

Read this document, it covers it

http://www.sophos.com/security/technical-papers/mac-data-theft.pdf

Ok great thanks guys.

Do a right-click on a file that you want to be private, do "get info", and check the "Locked" checkbox. Then nobody can edit it, not even you. Or even open it. Without your password, that is.