Warning: TrueCrypt is not secure. See this post for details and information on migrating to Bitlocker or FileVault.
TrueCrypt 6.0 was released on the 4th, and includes some great new features, including the ability to encrypt and hide the entire operating system for Windows users. It is also optimized for multiple-core processors.
TrueCrypt 6.0 is available for Windows, Apple OSX, and Linux. Get it here.
For first-time encrypters, last year I posted a tutorial on creating encrypted file containers with TrueCrypt. It is a bit old, since I was using TrueCrypt 4 for Windows, but it appears it is still accurate for the new version.