These three articles have a ton of stuff that I have found really insightful and help when it comes to being successful with iPhone Apps.
This is some analysis of guidelines created by Apple in an attempt to encourage more successful apps. Hint: when Apple is telling you how to make more successful apps you should probably listen. The articles covers these topics:
Marketing on the iPhone is not a defined field by any stretch of the imagination. But, as far as I can see this list does a pretty good job of telling you what is out there to help you get the word out about your app.
Selling ring tone apps has not proven to be a good business model. But, what about a free ad based ad? If you think you have a sticky app that many people would use if it were free you may make a ton of money with ads (and Apple will not get a 30% commission).