www.mollom.com



             The web is changing. User contribution is now what makes or breaks a site. Allowing users to react, participate and contribute while still keeping your site under control can be a huge challenge. Mollom is a web service that helps you identify content quality and, more importantly, helps you stop spam on your blog, social network or community website. When site moderation becomes easier, you have more time and energy to interact with your community. 
Top 5 benefits:
  • Kills comment, contact form and registration form spam
  • Overall content quality improved
  • Burden of site moderation reduced
  • Faster community growth
  • It's FREE!
 Top 5 features:
  • State of the art text filtering and content analysis
  • Works with all languages
  • Image and audio CAPTCHA service
  • Detailed statistics
  • High-availability infrastructure
Link: http://www.mollom.com/