www.truecrypt.org | Free
If your notebook contains sensitive information you wouldn’t want out in the wild should you lose your notebook, then you need to look into hard drive encryption. Once encrypted, your computer won’t boot without the proper password, and, better still, evildoers can’t even read your hard drive’s contents if they remove it and use another computer to look it over. Some notebooks and hard drives have this type of encryption built in at the hardware level, but for the rest of us, True-Crypt is a great alternative (and maybe even better).
Using AES, Twofish, or other military- grade encryption algorithms, TrueCrypt can encrypt either a “data section” of your hard drive, or if you prefer, the entire hard drive including the Windows boot partition. It can also create a second undetectable (and encrypted bootable) partition within the first, giving you a plausibly deniable area to store really, really secret stuff. Amazingly, there’s almost no slowdown when using TrueCrypt. Even its price is amazing— free.
Source of Information : CPU Computer Power User November 2010