TrueCrypt is powerful encryption software for your personal data. It works by creating creating a virtual hard drive within a file and mounts it, so your computer treats it as a real hard drive. You can choose to encrypt an entire hard drive, certain folders, or removable media such as a USB flash drive.
Encryption is automatic, real-time and transparent, so all the hard work is handled for you. It also provides two levels of plausible deniability, and supports various encryption algorithms depending on your needs, including AES-256, Serpent, and Twofish.