A couple I’d recommend…
Big Bang by Simon Singh
In Search of Schrodinger’s Cat by John Gribbin
For well-researched historical fiction which is also very amusing 
, try the Flashman series by George MacDonald Fraser.
Our ‘hero’ is a character from Tom Brown’s Schooldays, but you don’t need to read that. (Different author, different style.)
All you need to know is that Flashman is (spoilered just in case):
a bully, a liar, lustful, a good rider and with some talent for languages.
My recomendations for fun fast fiction, based on books I have recently read:
Christopher Moore:
I just finished Fluke, and it was great.
Lambwas even better.
Both very funny and very smart.
I also just read Jumper(ignore the movie exists) based on recommendations from the SDMB.
I can also second the Neil Stephenson suggestions. I found Snow Crash to be particularly well paced.
They’re somewhat dated now, and often hard to find, but I love the works of
Willy Ley
L. Sprague de Camp (His The Ancient Engineers is a classic, and Prometeus books still has his collection The Fringe of Science in print. )
Isaac Asimov wrote lots of science for the non-specialist, on the Slide Rule, The Brain, The Bloodstream, Electricity and Magnetism, etc. As I say, a lot of it’s out of print (but available via used-book stores and sites) and it’s out of date (but the basics don’t go out of style. His book on the slide rule is as accurate as ever, except that only enthusiats and fossils like me even know how a slide rule works)
James Burke – he doesn’t go in-depth, but his “Connections”-style works are always interesting, and he does keep coming up with new ones (the only one in this entry still alive and writing.)
I forgot to add that Labyrinth Books, a catalog and internet outlet for good scholarly books, is offering most of the American Presidents series for $5.98 each, a very good price for hardcovers.
You’ll be able to find many of the others books mentioned as well, though not always at such good prices.
So many books to choose from, but I’ll restrain myself. I’ll mention two histories, and three SF books:
Joseph Ellis’s Founding Brothers is a great, readable book on the Framers as they related to each other. Highly recommended.
James Flexner’s Washington: The Indispensable Man is the best one-volume bio of George Washington I’ve ever read. If you don’t know why he was a truly great man, you will after reading this.
George R.R. Martin’s Tuf Voyaging is a wonderful collection of interrelated science fiction short stories about starships, ecology, absolute power, war, and psionic cats. Beyond brilliant, and lots of acerbic, witty fun.
Joe Haldeman’s The Forever War and Tool of the Trade are just outstanding. The first is about an interstellar war that lasts for centuries; due to FTL travel and time dilation, two soldiers see it almost all the way through. The second book is about a Soviet mole in American academia in the 1980s who develops a mind-control device, and decides to put it to better use than his KGB handlers intend.
Read, and enjoy!
Another vote for Donald Westlake’s books. Most readers speak highly of the Dortmunder novels, which are very good, but the two I prefer are High Adventure and Dancing Aztecs, both involving counterfeit ethnic art, both very witty and well-paced.