I think the most common are probably Ad-supported, Subscription, and Freemium(especially for games).

As we're seeing with all the issues being brought up about Facebook, Twitter, and Zynga, these current models do not always work. And even when they do, there are still issues. There is huge potential right now for new revenue models, so I would recommend getting creative with how your idea could potentially make money. If app.net succeeds, then there will be more of a transition to subscription services versus free, ad-based services. Currently though, the majority of users prefer free. The challenge is figuring out how to make money from them, which is why ad-supported services are so prevalent.

So try something new. And don't be afraid to ask for money.