Amazon.com: Tapworthy: Designing Great iPhone Apps (9781449381653): Josh Clark: Books --- Josh is one of the most consensual voices in mobile UX and his book Tapworthy comes up on every question like this. Hear him out on the latest Web Ahead podcast to get an insight of what's in the book. Get it!

Josh Clark is an amazing voice in mobile UX. His book is the one that gets quoted the most in these types of questions.

This book is a fairly short read that is accessible to both technical and non-technical team members. It provides solid guidance for how to think about mobile and how to avoid some common and serious mistakes, as well as tips for providing a good overall experience. There are plenty of helpful case studies and lots of examples of the guidelines in action.

This book is a short read that is accessible to many of the stakeholders in a web design project. Though the parts that make the case for mobile might be old news, the most important things to keep in mind when designing mobile are just what a mobile-inexperienced team need to avoid some of the most serious mistakes. The book is filled with case studies and usable guidelines, with only a little bit of talk about programming code.

Amazon.com: Mobile Design Pattern Gallery: UI Patterns for Mobile Applications (9781449314323): Theresa Neil: Books --- In addition to Tapworthy mentioned by others, you should also check out Theresa Neil's new book which collects the best practices and patterns in mobile from across 100's of apps and across both iOS and Android.

When you're ready to drill down below top-level design and looking at actual coding, the Manning Book(s) on Android are a great reference. On the 3rd edition now, I've been impressed enough by each previous one to convince me to buy the next one. They are really giving O'Reilly a run for their money.