I'm currently working my way through these:
Clay Shirky, Here comes everybody. I'm only half way through, but this book is essential. A very nice analysis of how the crowds of the internet turns into well organized groups that can solve tasks that traditional organisations can't solve.
Dan Roam, The back of the napkin. A very nice book on how to use visuals to explain complex stuff.
Garr Reynolds, Presentation Zen. Currently the best book about presentation skills out there. Period.