wheel - 3:19 pm on May 25, 2010 (gmt 0)
I'm a believer that ads are best if they're perceived as content.
So my take would be don't bother with standard banner/text ads. Forget anything automated or on every page.
Instead, create something along the lines of a verbose directory, or pages with full descriptions.
For example, you have one section on 'search engine optimization firms'. Give the advertisers plenty of opportunity to talk about their services. Create another section or pages on analytics software.
Lots of content is better for WebmasterWorld, as the pages are likely to rank. It's better for the advertisers as it gives them targetted traffic and a chance to explain their services. And it's better for me because I can sit down and read about the product. Which is something I'm likely to do - whereas clicking on an ad is something I'm not likely to do.