Contact Form 7 Honeypot is a plugin by DaoByDesign that adds basic honeypot functionality to thwart spambots without the need for an ugly captcha to Contact Form 7. Contact Form 7 Honeypot introduces an additional field in the form that if filled out will cause the form not to validate an preventing spam.
“The principle of a honeypot is simple — bots are stupid. While some spam is hand-delivered, the vast majority is submitted by bots scripted in a specific (wide-scope) way to submit spam to the largest number of form types. In this way they somewhat blindly fill in fields, irregardless of whether the field should be filled in or not. This is how a honeypot catches the bot.”
Download and info: http://wordpress.org/extend/plugins/contact-form-7-honeypot/