How about using affiliate links for products that are relevant to your audience? E.g. books about programming, hardware, etc.. These can work surprisingly well

How about using affiliate links for products that are relevant to your audience? E.g. books about programming, hardware, etc.. These can work surprisingly well. As long as your content isn't a glorified advert, often your audience will be thankful for pointing out e.g. a book or website theme they weren't previously aware of even existing.