Develop forms, database coding and other things that make the site work
The most important thing you can have on your site is lots of relevant information -- information that solves a problem or answers a question for your visitors. This material should be enriched with lots of links.
The next most important thing you can have there is interactive features. These keep your visitors participating beyond their reading. Here are some ideas.
Use forms to gather information and to structure requests and signups.
If you've got a group that self-identifies, they'll probably use and benefit from a threaded discussion group. You can do this with a mailing list. If you do that, use a form for sign up. Or you can put a threaded discussion feature on your site.
People like surveys. You can put one on your site. Click here for an example.
People like to "play." For business users of the web, this doesn't mean "play games," at least not most of the time. I'm using play here in the psychological sense, the way children play. They have something they can try, and then they can see results. On financial sites, calculators perform this function. What you put on your site is limited only by your creativity and the abilities of your designer/developer.
Moving up the sophistication scale, you can provide features that personalize the experience on your site. These, again are limited only by your creativity and the abilities of your designer/developer. You can provide your users with personalized pages, product recommendations based on their expressed or demonstrated preferences and much more.