CryptoDisk is a powerful tool for creating and managing virtual encrypted disks encrypted volumes. It creates encrypted volume within a file on a hard drive or any external data storage device flash memory card, USB drive, etc and then mount it as a real disk. All the data are automatically encrypted using your password right before they are saved to disk or decrypted right before they are loaded, without any user intervention. Mounted volumes behave as real physical disk drives, however even when the volume is mounted, data stored in the volume is still encrypted.

Website: http://www.cryptodisk.com/