
Molecular Biology Made Simple and Fun https://www.amazon.com/dp/1889899070
You can't go wrong with Feynman's stuff. But his Lectures really are notorious for being the books that physics grad student wish were the standard primers, rather than books that are known to be easy for beginners to learn from. On the other hand, if you're gonna get lost, getting lost with Feynman is always more fun.
I've had good luck so far with the Very Short Introduction series -- specifically, the one on quantum mechanics didn't offend me too much, which says a lot. (Once you've actually learned a bit of real quantum mechanics the popular treatments will tend to drive you to drink.)
http://www.amazon.com/Quantum-Theory-Short-Introduction-Intr...
If you're looking for intellectual stimulation I wouldn't go toward medicine, per se. For practical medical skills I've been thinking of dabbling in first aid and EMS classes, but for intellectual stuff what you really want is biology and chemistry. I think it's been long enough since I last plugged Molecular Biology Made Simple and Fun on HN, so let me recommend it again:
http://www.amazon.com/Molecular-Biology-Made-Simple-Third/dp...
It's corny but the science is solid, and it is so much lighter, more readable, and cheaper than The Molecular Biology of the Cell, which is a classic text and a book that I still intend to read someday, by god, whenever I have something like three entire months of spare time and a very solidly designed reading desk. [1]
Incidentally, have you looked at the online courses you can get for free these days? The other day on MIT Open Courseware I found an intro biology course taught by none other than Bob Weinberg and Eric Lander:
http://ocw.mit.edu/OcwWeb/Biology/7-012Fall-2004/CourseHome/...
It's a bit tricky to listen to in the car, or even to watch, as the slides for this particular class are hard to see and some of the topics are necessarily visual. But, still, these guys are star professors for a reason.
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[1] Or when the Kindle version comes out. MBoC is a book designed for that big Kindle. If I tried to read the print version in bed I'd probably crush myself to death.
http://www.amazon.com/Molecular-Biology-Made-Simple-Third/dp...
Materials Science: Gordon, Structures, or Why Things Don't Fall Down.
Linguistics: Pinker, The Language Instinct
Evolutionary Biology: Dawkins, The Blind Watchmaker
Molecular Biology: David Clark, Molecular Biology Made Simple and Fun
Physics: the canonical answer is "Feynman". I won't argue with that. His little books (QED and The Character of Physical Law) are quite nice.
The science in the book is 100% serious, too, and at the approximate level of an intro course in college. I faked it for three years as a biophysics postdoc with the help of that book. Admittedly, the molecular biologists chuckled at my understanding of their field, the way you would chuckle at a precocious four-year-old, but at least I had a vague idea of what I didn't know.
Do not let its silly title fool you. This is an excellent book containing real biology facts. Plus, unlike Molecular Biology of the Cell, if this book falls on you from a high shelf you have a chance to survive.
Of course, the book predates siRNA. Nothing ages faster than a molecular biology book.