According to this Economist article, the two most notable paywall success stories are financial publications:

The two most prominent are the Financial Times, which lets web users view just a few articles each month before it asks them for money, and News Corp’s Wall Street Journal, which charges for much business and finance news.

In Slate, Jack Shafer tries to explain why only a few sites thrive behind paywalls:

Not all successful paid sites are alike, but they all share at least one of these attributes: 1) They are so amazing as to be irreplaceable. 2) They are beautifully designed and executed and extremely easy to use. 3) They are stupendously authoritative.

Good points to be sure. But maybe overlooking a more important lesson: The easiest way to get people to pay you money is when they think they’re getting something in return that will help them make more money.

FT and WSJ succeed because of the kind of information they deliver: financial analysis and info that enables its readers to invest wisely, manage a business better, and/or improve the bottom line.

It’s a lesson for anyone trying to figure out what to sell. Help people make more money and then forking over cash to you becomes a no-brainer. It’s not the only way to sell something. But it’s probably the easiest.