1 - Dating sites with targeted communities such as religious peers.<p>2 - Premium news sites. You see a lot of these with financial sites such as theflyonthewall.com, briefing.com etc.<p>3 - Quality tutorial sites. lynda.com<p>4 - I started paying up for an ad free experience and premium features for email.before gmail took off.<p>5 - Job listings on craigslist.<p>6 - Membership sites. Too many to list.
Netflix is the first example that springs to mind. They're not purely a web app, but they're the only thing I'm paying for besides 37signals. <p>I might pay one of these domain-name-brainstorming sites that are popping up, not sure yet. Buxfer.com also looks intriguing, not sure if they charge yet.