Although I promised myself that I wouldn't read anything that isn't Scottish - my job demands that I improve my knowledge of Scottish literature - I couldn't help but pick up and read Simon Singh's Big Bang, a history of how the Big Bang theory of the universe came to be. It's a long book, almost 500 pages, but very easy to read and it only took me a few days to finish it. I've read quite a bit of science books, so much of it was retreading old ground, but Singh writes in an easy, informal way, and he does like to explore the back-stories and personal characters of the scientists and explorers who have lead, from Ptolemy's Earth-centric view, to Copernicus, to Einstein, Hubble and beyond.
It's not rocket science, and it's not going to stretch your mind, but as an introduction to the Big Bang theory - and an introduction to how science works - I recommend it highly.