BestCrypt is an industry-strength encryption tool that applies a range of techniques to protect your most valuable files.
The program can quickly contain an encrypted container file, for instance, which is then mounted as a virtual drive on your PC. You'll be able to view it in Explorer, drag and drop files there, save documents to the container from applications, just as though it was a regular drive.
But in reality, it'll be encrypted with your choice of password and encryption algorithm (Triple DES, BLOWFISH-448, CAST, GOST, IDEA, RC6, AES (Rijndeal), SERPENT and TWOFISH are all supported), encryption mode, hash algorithm and more. Only you will be able to mount the drive, and once it's unmounted then any intruders won't even know it's there (and wouldn't be able to access it anyway).
If the encrypted container approach doesn't suit your needs, then you always create an encrypted archive with the bundled BCArchive tool. This works much like any archive handler: drag and drop whatever files you like onto the program, and it can save them to a single, self-extracting file. But this is a very securely encrypted file, no-one's going to view it without the password, which makes the system perfect when you need to email confidential data to someone.
You also get CryptoSwap, a utility that encrypts the Windows Swap File to ensure any document remnants it contains will stay private.
And BestCrypt also supports full volume encryption, the ability to encrypt an entire physical drive. That's an optional feature, though, and doubles the cost of the program to $119.95.