Kontak is a WordPress plugin by tekinoypi that is coded in HTML5 / CSS3 and has CAPTCHA that does not use PHP sessions. Messages are sent by email.
Features:
Coded in HTML5
Enable/Disable Captcha
Captcha is not using PHP sessions
Customizable fields:
Subject for email
FROM and TO email headers
(Optional) Customize CSS.
View demos:
http://racketroll.com/wp-plugins/
http://www.onegirlfactory.com/
Download: http://wordpress.org/extend/plugins/kontak/