Yup, you do have to sign up with most of them to see their advertisers.
I would suggest you either:
1. Search this forum's sigs and make a list of 10 affiliate programs people are boasting about. Then blindly sign up for all of them. Once you are approved for a few you can select what products you want to promote.
2. Decide what products you want to promote, post back some specifics and then maybe someone will point you in the right direction.
Whatever you choose, do it Today. The worst thing you can do in this biz is sit around and wonder.