By having a regular e-newsletter (weekly or monthly), you can stay top of mind with people. Plus, you can interact much easier with all people by putting hyperlinks to your website thereby making it easier for them to get more information on specific topics. By keep contenting on point and to a minimum, makes it interesting, enticing them to keep reading and look out for future issues.
Most importantly, you can see almost immediate and measurable results because you can monitor the stats and see what sections are the most clicked on allowing for testing and tweaking to see what your users prefer.
Overall, an e-newsletter is an cost effective way of marketing, and, if you keep it interesting, it will entice them to keep reading and look out for future issues.