Well, two quickies come to mind:
One is self-serving--I have a book called Higher Process that's about evaluatin self-help and productivity advice via paychological research. GTD is featured in several chapters. (http://www.amazon.com/Higher-Process...dp/B007Z739BS/).
I also started the year reading Susan Cain's QUIET. Very good book on introversion with implications for business, work style, education, productivity, etc. (http://www.amazon.com/gp/aw/d/0307352145/)