Douglas R. Hofstadter, Metamagical Themas: Questing for the Essence of Mind and Pattern (New York: Basic Books, 1986).
This book (revised again in 1996) is a collection of the columns Douglas Hofstadter wrote for Scientific American in 1981–83. The columns are grouped by topic and each is followed by a lengthy postscript that expands on the original column. He explores topics from self-referentiality to Rubic’s Cubes, from Lisp atoms to the nature of cognition. I found the final sections of the book that deal with cognition and identity to be the most provocative and engaging, though I thoroughly enjoyed the diversity of topics Hofstadter discusses.
If you’re looking for some stimulating reading in bite-sized chunks, you can’t do much better than this book. I highly recommend picking it up.