1. Publish your visitor's comments or questions that you receive via e-mail. Include your response for each comment. Just get their legal permission first.2. Interview experts or famous people your visitors would recognize. All you have to do is write out questions. Just publish interview on your site.
3. Place a discussion board on your web site. Your visitors would create content for you, but don't forget to participate on board too.
4. Accept guest articles related to theme of your web site. You could publish them when needed or combine them in a huge article directory.
5. Review products and services that your visitors might be interested in buying. Publish your opinions about them right on your web site.