I'm glad to see Cryptonomicon on the list. Looking back, that book has probably had the single greatest influence on my life so far. I've always liked computers, but don't think I'd be nearly involved with them as I am now had I not read it.
I've also heard great things about Measurement but haven't read it myself. Another great math book that I have read is Vector Calculus, Linear Algebra, and Differential Forms, though trying to get through that at 14 would probably be a bit disheartening.
Edited to add: Also, looking back I remember how stressed I was as a teenager because it seemed like there was so much to learn and I had on idea where to begin. I wish someone had told me it was okay to not know certain things. As I've gotten older I've become much more comfortable with learning things as I need them rather than assuming I need to learn everything ahead of time. This has made my life much less stressful and much more enjoyable.
Newer: Ancillary Justice. Really interesting ideas about the self. Over the years: Octavia Butler. Some very challenging ideas.
Honestly, though, I think 14-year-olds should read a lot of random crap from the library. Legal thrillers and historical romance and linguistics texts and home repair manuals and history of Thailand and books about sneakers, and the Tao Te Ching and that famous book about Buddha. Martin Luther King's Letter from a Birmingham Jail. That blew me away in 9th grade.
I've also heard great things about Measurement but haven't read it myself. Another great math book that I have read is Vector Calculus, Linear Algebra, and Differential Forms, though trying to get through that at 14 would probably be a bit disheartening.
Edited to add: Also, looking back I remember how stressed I was as a teenager because it seemed like there was so much to learn and I had on idea where to begin. I wish someone had told me it was okay to not know certain things. As I've gotten older I've become much more comfortable with learning things as I need them rather than assuming I need to learn everything ahead of time. This has made my life much less stressful and much more enjoyable.