Be informative and stay current
The incremental cost of providing more information for your customers is approximately zero, so don't be shy. The more information, education, and opinion the better!
Information that your customers want is great content that builds repeat traffic. The Search Engines love relevant content too!
Also keep in mind that the Internet is not a static medium. It's dynamic and so should be your business. Provide fresh content, new links, new information, redesign your site periodically, and ALWAYS think of new ways to create additional value on your site.
IF the information on your site doesn’t change why would someone come back?
Better yet, send them interesting information via an e-letter and you keep up the relationship on your terms. (more on that later)