We don't use ads for the D programming language. What we do, and I've done in the past, is write articles about programming that are interesting in their own right, and that happen to use D:

http://digitalmars.com/articles/

Pretty much all programming products, even free ones, operate this way. Much of the content you see on Hacker News, and on reddit/r/programming, is of this form.

There are TV shows that do the same thing, such as "Detroit Muscle". Each show is about how to do a repair/customization job on a car, and various tools and products are used to do it (and the makers of those tools and products pay for the show).

Tupperware parties are another example of this sort of thing.

It's like having a free cooking class where you show people how to cook with butter, and you're in the butter business.

The hit TV show "This Old House" was all paid for by the products and tools used in the show. It didn't look like advertising, but that's exactly what it was. And it works, and people love the show (I loved it, too).

I.e. organic marketing.

That is basically my plan for my next website. But some problem spaces are not served well by that model. Also, I think there is a substantial learning curve for doing something like that well and not being borderline con artist.