Are you looking for a WYSIWYG editor (what you see is what you get), for example like the one you see when you enter a post?
Seems you mean a script which sends out email with content in HTML form. Most scripting languages such as PHP, Perl, ASP, etc have built-in mail functions for ready use.
You may want to look at these too: http://www.arkie.net/~scripts/mailme/ http://www.stadtaus.com/en/php_scripts/formmail_script/ And I recommeded PHPMailer because its able to send mails in a variety of ways ( mail() function, sendmail, qmail or even direct SMTP ). It an also send HTML mails. Thomas