Tools for Creating App Mockups

Protocols
Strings
Custom URL Schemes
Saving Data

Sizes of iPhone UI Elements
The Status Bar - hiding; setting the color
UIAlertView - pop-up alert messages
UINavigationController
UIView - animating views

Checklist for submitting an app to the app store
Build your app for distribution
What to do when your app gets approved
Tracking App Usage and Sales

Setting up a web page for your app
Designing an iPhone-friendly Website
Promoting Your App

Apple's iPhone Dev Center is the place to go to become an iPhone developer.
Apple's iPhone Developer Forums are available to registered iPhone developers. These are a great place to find answers and get help.

MacRumors iPhone Programming Forum
iPhone Dev SDK Forum

iPhone Development Blog by Jeff LaMarche, author of the Beginning iPhone Development book.
Cocoa with Love - Matt Gallagher's Cocoa/iPhone programming blog, with example projects.
Theocacao - Scott Stevenson's Cocoa blog.
iPhone Developer Tips - more useful code snippets.
NSBlog by Mike Ash. His Friday Q&A postings cover some more technical C and Objective-C topics.

Conferences for iPhone Developers