This form will prevent the most common forms of automated "contact form spam" by adding a hidden field to the form. If any text is entered into the hidden field, the message is assumed to be spam and thrown out.
It also uses JavaScript to generate your email address as a clickable link after the page has loaded. This prevents scrapers that do not execute javascript from reading your email address.
It includes both a simple version and an advanced (pretty) version, you should only need to put one or the other on your website.
For a detailed explanation of the methods used, see http://nfriedly.com/techblog/2009/11/how-to-build-a-spam-free-contact-forms-without-captchas/
The MIT License (MIT)
Copyright (c) 2013 Nathan Friedly - http://nfriedly.com/
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.