Many online businesses have an affiliate program, in which the business pays a commission to publishers whose marketing efforts result in a sale, visitor signup, or other action for the business.
In most niches it's possible to find affiliate programs whose products or services are a good match for your targeted audience.
If you sell your own products (especially infoproducts or membership sites), you can run your own affiliate program and reward publishers who bring new customers to you.
Watch the video on ASC's Affiliate Program.