What's on your bookshelf?
makecheck: I appreciated "The Art of UNIX Programming" (ESR), because it clearly demonstrates the value of the "do one small thing well" approach to software.  While it's a bit of a refresher to Unix veterans, it still has lots of interesting examples of well-designed programs that uphold Unix design principles (e.g. flexible, simple, transparent).  I've seen plenty of developers over the years who've been "tainted" with the Monolithic Blob approach to software design, people who ought to read this book cover-to-cover.