Here is a great on by Elia Freedmon on his lessons learned with releasing an app into the app store -
http://eliainsider.com/2009/04/15/lessons-learned-one-month-in-the-iphone-appstore It is pretty in depth and insightful.
I would imagine the king of this model at the moment is Gameloft's Order & Chaos Online. It's basically a World of Warcraft MMO clone that has a 99 cent monthly subscription fee in addition to the initial purchase cost.
Here's an article on TouchArcade about how they supposedly raked in a cool million in the first 20 days.