Apple have published a set of beginner guides to help people new to iOS development. They cover everything from a tutorial on how to build your first app right through to articles on design patterns, interface design and uploading to the app store.
This is something I used to take advantage of when I was writing Mac apps but never took the time to research it on iOS. Matt Gemmell gives a good overview of the process and has some useful links to additional code and tools which will make using PDF images easier to deal with.
Talking of PDF icons, Peyton Randolph has a great UIView subclass for displaying masked icons from a single source image, or PDF.
Nik Burns on the settings URL schema which allowed deep linking into the settings app but which is unfortunately gone in iOS 5.1. Nik also has a radar number to dupe if you want to voice your opinion to Apple on this as well.