Rohos Mini Drive
The Rohos Mini Drive utility protects files on a USB drive by creating an encrypted and password-protected partition, or section of drive space. You can save or copy files into the partition as per normal, but if you happen to lose the drive anyone would have to know the password to decrypt your protected files.
After a quick download and installation you can choose a size, encryption type (AES256 or Blowfish) and drive letter to use for the encrypted partition. When you connect, or mount, the encrypted partition, it will show up in Explorer under the drive letter you choose. You can access the remaining, unencrypted space on the drive like you usually do, under the drive letter usually used for USB drives on your PC.
The handy tool is entirely portable. You can get to your encrypted files on another PC that doesn't have the Rohos Mini Drive software installed by going to that regular, unencrypted part of the drive and double-clicking the 'Rohos mini.exe' file and providing your password.
While the utility is active, you'll see a program icon in the system tray. When you want to disconnect the drive, be sure to right-click the icon and disconnect the drive to avoid damaging your files.
If you use USB drives to carry any sensitive files, Rohos Mini Drive is an easy and free option for keeping your data safe from prying eyes.
Note: This program is donationware. It is free to try, but the author accepts and encourages donations towards further development.