I agree with some of the others, that you should market products that are in the niche that you and/or your site is in. It always works best for more sales and conversions if you are marketing/promoting things that would most likely be of interest to the type of people (and their interests) that are seeing your offerings.
Offering things that are in the same or similar niche to that which you are in will most likely make you more money than trying to just market things that your audience will probably not be as interested in.