Recently I've read "Natural Acts" by David Quammen -a writer on natural history. Its a collection of his early essays and is quite good. I've also read "Song of the Dodo" by him-even better . Look up Quammen on Amazon
HERE.
Stephen Jay Gould was a great science essayist who frequently disagreed with a favorite here, Dawkins. A lot of vhis stuff isn't on Kindle, but you can check his work
HERE.
Dunno if "The Elegant Universe" was mentioned, but that was pretty ace. Looky here , the Kindle edition is only $2.11. Grab it
HERE.
On the same page is Isaacson's biography of Einstein. It was universally well regarded, and you might want to try it if you are an Einstein admirer (and which intelligent person isn't?)
"At the Water's Edge" by Carl Zimmer was superb, but its only avaiable as a pbook. He has a couple of newer ones , like "Brain Cuttings" and "Planet of Viruses" but I don't know how good they are. I'll check out the samples.