There are many different affiliate program directories available on the web. If you choose to use one, be sure that you choose a legitimate one. Many of them may prove to be unreliable.
One of the best ways to find a reliable directory is to ask someone who knows. If you know someone already in the affiliate business, ask them for a reputable affiliate directory recommendation. If you don't know anyone, join a couple of online discussion groups and ask around. When you find a discussion group that seems to be full of friendly and knowledgeable affiliate-related individuals, ask the group to recommend an affiliate marketing directory that covers your area of interest.