To start with, the Inmates are Running the Asylum by Alan Cooper is easily one of the best reads of the year for many reasons. First off, I think it will be one of those books that changes the way I do (or don't do) things: I'll try very hard in future to push interaction design up front on projects I can influence and try to persuade it into the hands of those most qualified to do it. I'll undoubtedly still be expected to do some interaction design myself (sorry Alan!) but I'll be using personas much more to help me do this. Secondly, it was a very enjoyable read and quite hard to put down. There's a strong possibility that I enjoyed it because I sympathise with the author on his strongly held views about the nature of software development and software developers in general though and I realise this makes my opinion quite biased.
I read The Pragmatic Programmer by Andrew Hunt and David Thomas about a year ago and thoroughly enjoyed it. This book falls into the "made me happier in what I do" category and I specifically remember writing a quick review on our wiki at work, recommending this book for anyone feeling a bit disillusioned with software development. It's an excellent compendium of ideas, practices and patterns for becoming a successful developer that will probably not age. One slight caveat is that you must forgive the authors' obvious lean towards command line tools and away from anything with a GUI, as being "part of their upbringing" on Unix.
User Stories Applied: for Agile Software Development was the second of Mike Cohn's books that I have read and was just as good, if not better than the first (Agile Estimating and Planning). What I liked about this book was the clear summary at the end of each chapter, with a run-down of everyone's responsibilities in the process. I'd recommend this book to developers, project managers and product managers to help them understand how to deliver value through an Agile project.
Finally, 5S Kaizen in 90 Minutes by Andrew Scotchmer was, as the title suggests, an enjoyable quick read that has whetted my appetite for understanding of the values that make Toyota one of the most successful manufacturers in the World.