Programming in the 1990s by Edward Cohen. A rather practical introduction to the calculation of programs from their specifications. Plenty of introductions to computer programming involve guessing your program into existence. This is one of those rare books that give a solid, pragmatic approach (with examples) of developing software from solid, mathematically sound specifications and avoiding errors by design.

Even if you don't adopt formal methods in your day-to-day work (often we're not building sky-scrapers) it's a useful book to give you insight into the kinds of questions one should be asking and thinking about when designing software systems.