Truecrypt is nice but you need admin rights to the computer you are using to get it to work properly, which would not work on a public computer or one that you do not have admin access.
I personally have an Ironkey usb flash drive. It is a very nice little guy
I encrypt the text files containing license keys for S/W I resell, using DsCrypt. It's portable and securely erases the original file when it encrypts it. No need to encrypt everything on the flash drive.
I haven't used trucrypt yet. I have heard about it a lot but never felt the need for it. Maybe if it had customer data on I might but not for simple portables and install files.