One that come to mind that might be making a profit: Mint.com
Mint also gives the managers at Intuit nightmares.
They automatically suggest [= scales with no marginal effort] financial products which they claim are good fits for the users (who are not the customers). For example, they might say "You're paying $X in interest a month with your current credit card Y. If you were to switch to credit card Z, you would only be paying $Q, saving you $P a month."
Credit card Z then pays them an affiliate commission for the lead. The issuer of credit card Z is the actual customer.
It's really all about extremely targeted but transparent marketing as well as finding interesting ways to utilize user data. The data and its interpretation is what is really valuable, and that is what the customers are paying for. It cant just be simple advertising though, it has to resolve a shared necessity of both customer and user.