If you're looking for a very simple way to protect the privacy of your e-mail communications, look no further than Easy Email Encryption Lite ($18, demo). It provides about an easy a way to encrypt communications as you'll be able to find--as long as the receiver has a copy of the program as well.
To encrypt a message that you want to send, copy it into the program, tell the program to do the encryption, and it copies the garbled, encrypted text to your clipboard. Simply copy the encrypted text into an email message and send it along. The recipient can then copy the encrypted text to their Windows clipboard, and have Easy Email Encryption Lite decrypt it. That requires, though, that both sender and recipient agree on the key to use.
You can use keys of between 16 and 64 characters, and the longer the key, the more secure will be the communications. The software uses an encryption method called Cryptosystem ME6, which was created by the Easy Email Encryption Lite's developer, Hermetic Systems.
The downside to Easy Email Encryption Lite is that both user and sender need to use the same software. By way of contrast, an encryption standard such as OpenPGP allows people to use different software, but the same standard.
If there are one or two people with whom you often share e-mails that you want to keep private, Easy Email Encryption Lite is a simple solution. It's not overly technical, and makes it easy for anyone to encrypt communications. And if you have valuable information that you need to keep private, $18 isn't too high a price to pay.