I can't choose a single design book as my "favourite," but this one's up there: Graphic Design as a Second Language, by Bob Gill.
"The only way to tell which jobs Gill designed yesterday and which ones were designed years ago, is to look at the date. Styles come and go, but his ideas and teaching philosophy are timeless. That's why Bob Gill is one of the heroes that got me and so many others into graphic design in the first place."
— Michael Bierut
If you're interested in graphic design, the book's definitely worth a read. A little off-topic, turns out that Gill went on to direct a porn movie called The Double Exposure of Holly. David the designer shared that, but does go on to say he hasn't seen it, obviously. David's just a fountain of knowledge.
A few more good books.