One of five completely random ad networks I found:

Reaching the Unmotivated
Advertisers are usually obsessed with active consumers, like people in the market for a car or shopping for a certain product. But let’s face it: There are plenty of apathetic consumers out there who also need to be reached. That’s where 420Click.com comes in, offering advertisers the opportunity to reach “marijuana friendly people.” It makes sense. After all, “High Times” has been around for 38 years. The company boasts of “thousands of marijuana websites and blogs” in its network and targets people already interested in marijuana services and products. In fact, on its website, the company says it has strict policies of what kinds of sites the ads will be placed on. “To ensure the quality of the network, only websites with marijuana content can display ads and 420click.com reviews all websites for compliance.” Advertisers have the ability to set how much they want to spend per day as well as per click. Pass the Doritos.

Click through to see what other niche audiences ad networks target. Some, let’s say, interesting ones.