Letters to a Young Scientist
Edward O. Wilson
Science, biography, essays
A love letter to science, framed as epistles to an imaginary recipient. Letters to a Young Scientists is beautifully if simply written and often quite touching. It really gives a wonderful feel for how much Wilson adores science--indeed, for the love that any good scientist feels--as well as giving some of Wilson's own biography. (Incidentally, there are also many fascinating facts about ants.)
If you're a scientist, or if you're interested in how scientists feel about what they do, this is the book for you. If you're not interested, you should maybe read it anyway; you may well be fascinated before you finish.