Rockable Press has just released a great looking book on iPhone Apps and Entrepreneurship.
Most of their books have been outstanding, so I just wanted to point it out and make sure you took a look if you were even interested:
This book provides you with the knowledge and the techniques you need to spot a great opportunity, get the most from the App Store, make smart decisions about development, craft a stunning interface, and promote your app successfully!
Drawing from the insights and experiences of 16 top-notch app developers, and survey responses from over 1000 iPhone users, David Appleyard equips you with everything you need to successfully become an iPhone app entrepreneur!
Might just be worth less than $20 bucks.