Managing the Professional Service Firm by David Maister. I can't keep this one on my shelf because I keep giving it away.
Cryptography Engineering by Bruce Schneier. Very accessible. Probably not very practical if you're not building a cryptosystem, but it's a nice way to get a lay understanding---and scare you enough about how many pitfalls there are. When you finish read this loving criticism also: http://sockpuppet.org/blog/2013/07/22/applied-practical-cryp...
Forever Undecided by Raymond Smullyan. Fun "puzzle guide to Gödel". Out of print but Amazon has used copies.
Quantum Computing since Democritus by Scott Aaronson. Fun survey but requires some familiarity with P/NP, quantum mechanics, linear algebra.
Programmers at Work by Susan Lammers. Interviews with computer pioneers. Interesting to see how they think and what they have in common.
Time Management for System Administrators by Thomas Limoncelli. Short, easy read with lots of practical advice for all of us.
The Mac is Not a Typewriter by Robin Williams. Very slim. Learn the difference between hyphens, en-dashes, and em-dashes.
If you do product design you might enjoy a slow musing read through Apple's original Human Interface Guidelines.
Those last three combined probably weigh half of the Tufte book.
Have a nice vacation! :-)
Design of every things by Don Norman
Reinventing Organizations - A guide to creating organizations inspired by the next stage of human consciousness (Pay what you want book) http://www.reinventingorganizations.com/
How to Create a Mind: The Secret of Human Thought Revealed, by Ray Kurzweil
http://amazon.decenturl.com/make-a-mind
Program or Be Programmed: Ten Commands for a Digital Age, by Douglas Rushkoff
http://amazon.decenturl.com/ten-commands
Cool Tools, by Kevin Kelly
http://amazon.decenturl.com/cool-tools
(Yes, those are affiliate links)
Zero to One
Starts with why
EMyth revisited