As I understand your question, you want to act as an affiliate and are looking for businesses that have programs you can tap into. (Conversely, you may mean that you are looking for affiliate partners to promote your site, but I'll focus on the first question.)
Merchants (the seller) and affiliates (sites that promote the merchants) typically come together through affiliate networks. These are clearing houses that match affiliates and merchants, provide third party tracking and may manage the payments.
There are several reputable networks, including:
Commission Junction
Pepper Jam
Directtrack
As an affiliate, you'll find tools for ranking merchants, etc.
As a merchant, these give you access to a vast range of potential affiliates.
Steve Adams is vice president of marketing for
Protus, a provider of Web-based services for small- to medium-size businesses. He is a seasoned industry speaker having spoken at a variety of telecommunication trade shows and conferences. He is a graduate of the University of Waterloo and the Ivey School of Business.