Mac OS X only: Cryptor is a free, dead simple encryption utility for OS X that protects any file or folder from prying eyes. All it takes is a drag and drop, a password, and that — ahem — private media is password protected.
If you want to encrypt the occasional file or folder in OS X, then OS X's built-in FileVault tool is overkill (it encrypts your whole home folder), and even TrueCrypt can be overly complicated. That's where Cryptor comes in.
Using Cryptor, you can encrypt and password protect any files or folders in a jiffy. Drag the stuff you want to encrypt into Cryptor, click the Lock, enter a password (and hint, if you like), and it quickly encrypts the file to a new file with a .damn extension (e.g., Top Secret.damn) using whatever encryption method you choose. (It supports Blowfish, RC2/4/5, DES, and AES 128/192/256-bit.) When you want to access the files, double-click the .damn file, enter your password, and you're in business.
Cryptor is a free download, Mac OS X only. Got a preferred encryption tool? Share it in the comments.