I searched Search YC and did a site-restricted search of HN on Google to look for previous threads on best books. New participants have joined since the last thread was active, so I'll ask here for suggestions of books that delight the mind, and I'll include some previous suggestions. I will intentionally omit books that don't purport to be nonfiction, just to emphasize the nonfiction titles that are so neglected by so many Web-based best book lists. All of your further suggestions are very welcome.
Mindset, by Carol Dweck. As one HN reader commented, "It'll change the way you think about the way you think." Highly recommended.
Language in Thought and Action by S. I. Hayakawa.
How to Read a Book by Mortimer Adler.
Envisioning Information by Edward Tufte.
Fooled By Randomness by Nassim Taleb.
E. W. Bovill's English Country Life 1780-1830 was recommended by pg a while ago.
My favorite so far this year is What Intelligence Tests Miss by Keith Stanovich (2009).
http://yalepress.yale.edu/yupbooks/book.asp?isbn=9780300123852
http://www.amazon.com/What-Intelligence-Tests-Miss-Psychology/dp/030012385X/
My favorite book I read in 2007 was What Is Intelligence by James R. Flynn, which is just about to come out in a new expanded edition (2009).
http://www.amazon.com/What-Intelligence-Expanded-PB-Beyond/dp/0521741475/
My favorite book I read in 2008 was The Nature of Paleolithic Art, by R. Dale Guthrie (published 2006).
http://www.amazon.com/Nature-Paleolithic-Art-Dale-Guthrie/dp/0226311260/
The Road to Reality: A Complete Guide to the Laws of the Universe, by Roger Penrose.
The Feynman Lectures on Physics. Lots of HN readers suggest reading lots of Feynman, and I agree.
Godel Escher Bach: An Eternal Golden Braid has been recommended by multiple HN readers in most threads like this.
Robert Pirsig's book Zen and the Art of Motorcycle Maintenance.
How Buildings Learn by Stewart Brand.
Founders at Work by Jessica Livingston.
Tipping Point by Malcom Gladwell.
Freakonomics, by Levitt and Dubner.
Against the Gods by Peter Bernstein.
The art of war by Sun Tzu.
The 33 Strategies of War by Robert Greene.
The Design of Everyday Things (formerly The Psychology of Everyday Things) by Donald Norman.
Many HN readers recommend Structure and Interpretation of Computer Programs (SICP) and I heartily agree with that recommendation.
Code by Charles Petzold.
Introduction to Algorithms by Cormen/Leiserson/Rivest/Stein (CLRS).
Code Complete by Steve McConnnell.
The Mythical Man Month by Fred Brooks is a very thoughtful book.
Statistics: A Guide to the Unknown by Roxy Peck, George Casella, George W. Cobb, and Roger Hoerl.
Introduction to the Practice of Statistics by David S. Moore and George P. McCabe.
Workshop Statistics: Discovery with Data by Allan J. Rossman and Beth Chance.