iOS Animations by Tutorials Second Edition: iOS 9 & Swift 2 Edition Paperback – September 23, 2015

Really good book on iOS animations. I think the best for a wide range of practical animations. Marin is also great to follow on twitter. And he has a free monthly email with more animations. He obviously really cares about his work. I've been doing iOS work for years, but never did much with animation, and I have learned a lot.