CryptoMail.org - Offers free web based secure e-mail accounts. They additionally offer a secure open source client/server email system. - http://www.cryptomail.org
Red Amber Scrambler - DHTML message scrambler using the Vigenere method. - http://www.redamber.com/Scrambler.asp
Hushmail - Completely secure and encrypted, easy-to-use web-based email. Uses a Java applet. - http://www.hushmail.com