First look for an affiliate program that makes the effort you put into a sale worthwhile. Amazon.com has an affiliate program that is very popular, but the payouts are relatively small compared to other affilaite programs. You'll get a $3 payout on a $20 book sale. The number one rule of selling is that is just as hard to sell a $20 product as it is a $200 product, so shoot for a program that gives you better payouts.

Also research the program to make sure that you'll get paid for your work. For example, choose a program that makes a customer that buys from you a customer for life, not just for the first time they click-thru your site. See if the program places cookies on the visitors computer so they can track who your customers are. A good place to check for top affiliate programs is Commission Junction. They offer all kinds of different products and are a very reputable affiliate directory. Clickbank is also another excellent site for affiliate programs. I've listed some high-payout, reliable affiliate programs in my business opportunities section.