Daemon reminds me of Neal Stephenson at the top of his game. I just recently re-read Daemon and loved it just as much as the first time. A pulse-pounding mystery/techno-thriller with lots of actual technology thrown in. His characters use real-world hacks to attack networks and computers, like SQL injection.
Unfortunately the second book, Freedom, was a radically different type of story. And it was too removed from reality to be as exciting as Daemon.
The Education of T.C. Mits: What modern mathematics means to you, by Lillian R. Lieber.
This book explains non-Euclidean geometry, along with other math, in a way that just makes sense. It has a recommendation from Albert Einstein.
Lead me not into temptation... I can find it myself.