Generally, you will get the best referral traffic from pages that themselves get a lot of traffic. If you are able to get in touch with a member of the press, getting a link on a news site can be good for traffic, and good for SEO as well. Since you are selling something, then you would want to find sites that receive a lot of traffic in your niche. Most people don't take enough time to do the research to find the best niche specific site, and what's more it can take time to build a relationship with the people in the niche. The worthwhile referral traffic is going to be a result of you having cultivated a good reputation over time. Start now!