The first thing that you should be on the lookout for is if a company wants to charge you a fee for becoming a member. Most of these types of companies are Network Marketing or "pyramid schemes". I have nothing personal against "some" Network Marketing companies, as some of them do provide a good service or product. Actually, the Network Marketing business model is fantastic, if the rest of the world would just grasp it. Anyway, I'm getting off topic, but my point is that there are many companies that have given Network Marketing or "Multi-Level" Marketing a bad name so be very careful. That's not what you're looking for.

A legitimate affiliate program won't try to charge you a fee. They'll actually do pretty much everything they can to help you succeed because they realize that your success is their success too. This makes complete sense. Here are a couple reputable affiliate networks you can join that are excellent.

Commission Junction - www.cj.com

These guys are probably one of the most popular affiliate networks and are very reputable. They specialize in hard goods/physical products, but also offer service related merchants and business to business. The CJ interface can be challenging to navigate at first, but once you figure it out it's a breeze. Highly recommended.

Linkshare - www.linkshare.com

Also highly recommended. These guys have really taken off over the past few years and are giving CJ a run for their money. They sold out to a Japanese firm for over $400 million dollars several months ago and have since attracted many new major vendors.

There are several more like these two, but this should get you on the right track. Make certain to take advantage of CJU (Commission Junction University) as it's another great place to learn the basics of affiliate marketing. After studying a bit more, finding a good internet marketing affiliate program will be a breeze for you. I hope this helps you out.