FreeOTFE is a free, open source, "on-the-fly" (OTFE) transparent disk encryption program. Using this software, you can create one or more "virtual disks" on your PC - anything written to which will be automatically, and securely, encrypted before being stored. Many features included, with both PC and PDA versions available.
StrongDisk Pro enables to keep sensitive data on virtual encrypted disk, which works as a common disk, but all its content is encrypted on-the-fly. To mount protected disk a password and an external key is required. Any files, documents, tables and databases can be kept on and opened directly from encrypted disks. The content of encrypted disk is physically stored in a common file that enables to make backup copies easily.