Commission Junction
This is oldest and bestknown affiliate program. Very powerfull design and reports. They send money very fast and the are serious. Many webmasters is using this company....
This is classic way how to earn fast money but you have to at first sell online some goods or services from link leading to advertisers page. If your visitor buy nothing you earn nothing too. You can make up to 60% from that transaction. Adult business and adult affiliate programs have highest percentage and it is easier to increase traffic in adult industry. However, there are always other niches which are profitable as well.