From TrueCrypt Foundation:
With TrueCrypt for Linux, you can protect your sensitive data. This is free open-source disk encryption software. Creates a virtual encrypted disk within a file and mount it as a real disk. Encrypt an entire hard disk partition or a device, such as USB flash drive. Automatically and transparently encrypt in real time.
TrueCrypt for Linux provides two levels of plausible deniability. TrueCrypt uses encryption algorithms AES-256, Blowfish (448-bit key), CAST5, Serpent, Triple DES, and Twofish.