There are many available nowadays, on all sorts of subjects.
Absolutely anything by Peter Medawar, possibly the finest popular science writer of any time. Not a bad scientist either if his Nobel Prize is anything to go by)
Incidentally, I just a day or so ago recommended "Why the sky is blue" byG.Hoeppe. (It goes beyond the blue!)
Anything by Richard Dawkins, but especially the 2nd or 3rd ed of "The Selfish Gene" (don't judge it by the title!!!) "River Out of Eden", "Climbing Mount Improbable".
J.E.Gordon "Structures, Or why things don't fall down"
"Our Wandering Continents" Alex du Toit
"Cats' paws and Catapults" Steven Vogel
"The Invisible Gorilla " C.Chabris & D Simons
"Soap Bubbles" C.V. Boys (recently appeared on Gutenberg too!)
"Science for the Citizen" Lancelot Hogben
I.M.Copi & C.Cohen "Introduction to Logic"
"Fragments of Science" J.Tyndall (also on Guteberg)
Peter S. Stevens "Patterns in Nature"
Anything by E.R. Tufte, eg "Envisioning Information" & "The Visual Display of Quantitative Information"
Anything by John Maynard Smith, including "Did Darwin Get it Right?" and "The Origin of Life"
Anything by E. O. Wilson, even if you read some items with reservations.
Ditto Martin Gardner.
David Kahn, "The Code Breakers"
Harold Gatty "Nature is Your Guide"
David Attenborough's books, though they may look a bit coffee-tabley, are really very good material and very entertaining.
Steven Pinker's books have come in for a lot of flak, but I read as many of them as I can. They always have a lot of solid stuff to assimilate, and until the critics can do better, I reckon that he is the best writer among the experimental psychologists.
Some controversial old favourites are by Konrad Lorenz: "King Solomon's Ring", "Man Meets Dog" and "On Aggression".
Absolutely anything by R.V. Jones, such as "Reflections on Intelligence" and "Most Secret War".
"Metamagical Themas" and "Goedel, Escher, Bach" by Douglas Hofstadter and with Daniel Dennett: "The Mind's I" (A reall mind and eye stretcher that one!)
Dennett also wrote "Darwin's Dangerous Idea", possibly the best introduction to evolution by a non-biologist.
Oliver Sacks produced a mixed bag, but I have not yet read any of his works that I did not profit by. Try "Seeing Voices", "Musicophilia" and "The Island of the Colour Blind"
Roger Penrose wrote some fine books. "The Road to Reality" is not so much to be read as to be worked through, but it is very rewarding.
On a similar scale, Donald Knuth wrote some terrific material on maths and programming.
Anything by Daniel J. Boorstin! ("The Discoverers", "The Creators", Lots more!")
Etc... This was a glance round my bookshelves, and omitted a lot of good stuff that I missed or that didn't seem to fit in.
And oh yes, what about Faraday?