EDIT: The link didn't link correctly. Here it is: http://www.secret-solutions.com/download/other/BodyLanguagebyAllanPease.pdf

EDIT2: On top of Allan Pease's book which you should READ THROUGH, not skim. Here is a reference book which is basically an ENCYCLOPEDIA of body language and ALL nonverbal communication with links to chapters and everything. It's fucking incredible. I'd only use this as a REFERENCE MANUAL, NOT A READ THROUGH. But do what thou wilt: www.muphin.net/poker/E-Books/David.Givens-Body.Language.pdf

This is a book about body language by Allan Pease written in the late 1980's. There are probably books out there people perceive as being better and will suggest to read before reading this one but this book was everything for me. It was what initiated my faith in psychology as a useful science and what started my beginning of a new me. This is what catapulted me into the PUA community.

More Direct: This book is all about body language and offers pictures on nearly everything it discusses making learning 10x easier. There might be better books out there but this is all I ever really needed for a good understanding of body language. Misreads are very easy at first but after a while of applying this knowledge it's amazing the advantage it gives in social interactions and how much your awareness increases. There's not much else on body language that I've read that isn't covered in this book. It's a bit old but extremely accurate and powerful. And free.

Think you know all there is to know about body language and haven't actually read an entire book through? Think again.