All you're going to do is get people saying "Promote my product". It's a conflict of interest really asking here. The reason it's a stupid question is because you should sell a product related to the content of your site. If your site(s) are about fitness, selling ebooks on natural remedies for getting rid of diaper rashes isn't going to fly. If you haven't made a site yet, you can always go into niches that you're interested in or you have a lot to talk about. Others may advise you to go into niches that the money is in like "how to make money", weight loss, building muscle, marketing, pets, self-help, etc. You have to choose a product based on what the visitors of your site are going to buy. It's just as simple as that.
Thanks for replying I have tried selling relevant products but I've got 500+ hops and 0 sales on them. So I assumed the products were poor performers. Are there any sites out there that list the best performing affiliates for each category?
There isn't really anything. You can go by gravity, but that really isn't going to indicate how well things sell for you. I've had a piss poor time selling some high gravity products and an easier time for others. Over the last little while a 25 gravity product has been getting a lot of sales. I have another that has a gravity of 5 that has been selling consistently for months. I made a post on my blog about creating a database of timeless products for people to sell. I haven't compiled anything since I don't have much of anything to put up. Maybe someday it'll grow into something.