Chaturbate - Sign up to Chaturbate as a cam model. One of the largest cam sites in the world, based on an open free model where users tip with tokens and you can also do private shows to earn.
Streamate - Streamate is another huge cam site that you can make a lot of money with through gold shows and exclusive/private shows.
Stripchat - Stripchat is a somewhat newer cam site that has really blown up lately. It's a great layout with a more mobile feel to it. Tons of paying customers, so easy to make money.