Web-Based

CipherSend
System that allows your website visitors to send you secure email. Doesn't reveal your email address, thus preventing harvesting by spambots.
http://www.ciphersend.com

KeptPrivate.com
A secure web-based email service which offers encrypted message storage. KeptPrivate also offers secure POP/IMAP access.
http://www.keptprivate.com

MarineNet Radio
Providers of wireless internet e-mail messaging globally via marine SSB radio.
http://www.marinenet.net

Securenym
A secure, anonymous commercial email service.
http://www.securenym.net

Self Destructing Email
Send email which automatically deletes itself after reading and prevents printing, copying, saving, and forwarding. Unrestricted free trial; subscription thereafter.
http://www.selfdestructing.com/

Shushmail.com
Encrypted email solutions for business and personal use. Web-based, POP and IMAP capabilities all served using 128 bit SSL. 25mb quota.
http://www.shushmail.com