While XKCD is most known for being a webcomic, Randall Munroe, in 2009, published his work in a charming print collection. At times a romantic and at other times a scientist, Munroe succeeds in creating many "aha" moments for his readers. Why should you buy the book rather than just read it online? Because the book is filled with extras.
XKCD Volume Zero
The first extra is the page numbering system, which is neither base 10 (the normal system people use for numbering things), nor the next obvious choice, binary (what computers use, and Munroe does do a lot of geeky jokes) but rather an obscure system known as skew binary (Warning. The link explaining skew binary includes lots of maths)
Furthermore, many pages have various doodles, commentary and puzzles printed in red, as opposed to the normal black and white for this particular comic strip. It is the puzzles that really make the book worth buying, very few of which I can solve, but which reference all sorts of things from geekdom, including Star Trek, Ender's Game, Futurama, Binary, QR Codes, and much more.