LeeLu EncryptThat provides you with a portable encryption/decryption app that works right from the context menu.

This is a simple little program that will help keep your private files encrypted and safe from prying eyes. As with any type of encryption software, you must keep in mind that nothing in this day and age is impervious to intrusion but you can make it more difficult for interlopers to gain access to specific files.

Once you have it all setup, you will need to select a passphrase with up to 37 characters after you click encrypt/decrypt - remember your passphrase or you will be locked out of your own files.

LeeLu also has a handy AIO suite that includes a number of other useful tools that can be downloaded here: http://www.majorgeeks.com/files/details/leelu_soft.html