1) Make it an information type product. This can include online services. In my opinion, information products offer the greatest profit potential on the Internet. Think about it - There's no inventory, no shipping hassles, and barely any customer service. If the customer isn't happy, they get a refund. But you say, "I'm just an affiliate marketer. Why does that affect me anyway?" Simple. If the company providing the product has hardly any overhead, that leaves more to pay you, in affiliate commissions. I've seen information products paying affiliates as much as 50-70%, or more! Some experts would tell you to find a niche, then market to that niche. I personally prefer to find products that appeal to a wider audience. The choice is totally up to you.
2) The second key to finding the ultimate online affiliate program is residual income. Residual income is what creates real wealth. Make one sale, get paid again and again, without even making another sale. Which would you rather do, spend the time and money on promotion to get paid once, or time after time for years, or even the rest of your life? Subscription based products, such as web hosting and paid newsletters are ideal. Not quite sure what web hosting is? Web hosting enables you to put your website out on the World Wide Web for everyone to see. A hosting server stores your website files, and then serves them to the Internet so that when people type in your domain or web address, they see the website that you created. All websites need to be hosted somewhere. Maybe you could sell subscriptions to someone else's newsletter, and recieve a commisson. There also are dozens and dozens of membership sites that collect a monthly fee out there. Find one that appeals to you.
3) The third, and most important key in finding the ultimate online affiliate program is your passion. We all would like our life to feel purposeful. We want to feel passionate about what we're doing, to be excited about how we spend our days, to love our life and to feel we're making some valuable contribution. What's your passion? Be honest with yourself. What do you spend your time doing? What do you spend your money on? Maybe you've purchased a product yourself that you can't stop telling others about. Check into it. Ask if they have an affiliate program. You could be earning a commission for doing what you're already doing for free! If you find a product that lets your passion shine through, suddenly it's not work anymore, it's fun! When you are truly passionate about something, you don't have to try hard. It's engaging, it's exciting. When challenges arise, they can't deter you. They might slow you down a bit, but they can't stop you!
Finding an affiliate program that is an information product, produces residual income, and combine it with your passion and you will have found the "ultimate affiliate program" for you to promote.