It seems like there are 2 models. 1) Provide advertising users really want resulting in clicks 2) Provide a service to important to consumers/businesses they can't live without it and are willing to pay for it
Right now mostly everyone is working on 1) by trying to be the company who can sell another business a "guaranteed" customer.
A few companies (like 37signals) are working on 2) but that's much harder for a number of reasons. Until the internet is more embedded in our lives it's harder to provide a concrete value. Because the internet is so friction-less it's very easy for someone to compete with you reducing your share of a small market. Finally even now it's mostly middle class to upper class people with good internet access, dramatically reducing the market size (Exxon obviously sell to everyone).