The Passionate Programmer: Creating a Remarkable Career in Software Development (Chad Fowler) and The Pragmatic Programmer (Andrew Hunt and David Thomas).

I wish I had read The Pragmatic Programmer earlier in my career as it provides an excellent overview of many good practices in software development. Reading this a couple of years ago would have avoided/shortened many a learning experience.

The Passionate Programmer is a truly inspiring book, and comes highly recommended if you,

a) Feel that your career is in a lull, or
b) Need guidance in evolving your career as a software developer.