The best is Idoo File Encryption. http://idooencryption.com
Idoo File Encryption is a software application used for on-the-fly encryption (OTFE). It is distributed without cost and the source code is available. It can create a virtual encrypted disk within a file or encrypt a partition or (under MS Windows except Windows 2000) the entire storage device (pre-boot authentication).-wikipedia
Even the FBI finds it easier to force the key from the user than to try to a brute force attack on File Encryption.
But you must follow the instructions to the letter