First published in 1963, Peter Elbow's classic Writing Without Teachers has guided generations of students, business writers, and aspiring creative writers in turning raw thought into finished writing.  The 25th anniversary edition, published in 1998, predates the current emphasis on digital writing—nothing on blogs, websites, and such, I'm afraid.  But anybody who hopes to write, whether a novel, a work of criticism, or just the best possible e-mails and letters to the editor, should take the time to read this straightforward, unpretentious guide.
Though famous from the 1941 film noir starring Humphrey Bogart, Dashiell Hammett's original version of The Maltese Falcon takes on much darker, more nuanced themes than director John Huston would have dared in the Hays Office heyday.  Hammett presents law enforcement and its close cousin, private detecting, as grim, adversarial worlds colored by dogged persistence ad hoc morality.  Though some of the language seems contrived by our standards, this book remains both notably current and brutally realistic.
On Friday, November 19, 2004, Senior Sergeant Chris Hurley, at the end of his second year in the Aboriginal settlement at Palm Island, off Australia's Queensland coast, arrested Cameron Doomadgee for cursing at him and another officer. Doomadgee was drunk at ten in the morning. Forty minutes later, Doomadgee was dead, with injuries consistent with a massive car crash. In a feat of intense literary journalism, Australian writer Chloe Hooper tries to reconstruct those forty minutes, and the legal wrangling that lasts for nearly three years afterward.
Dietrich Bonhoeffer is primarily known internationally for his  Nazi resistance, which so thoroughly offended Hitler that, as one of his last doomed acts, the Fuhrer ordered Bonhoeffer hung before the Allies could free him.  But this book, difficult but readable, reveals him as a great church theologian, calling Christians to greater fidelity to Scripture.  Too often, we want to follow God at no cost, but Bonhoeffer says this confuses the starting point with the finish line.  The Cost of Discipleship demands slow savoring, not hasty reading like the latest potboiler.
One desperate live-in maid accepts a job caring for an invalid mathematician.  She needs a man to shape life for herself and her son, while her family gives him purpose.  But an old injury has scarred the mathematician: his memory only extends back eighty minutes.  Readers have grown cynical on big-hearted stories of family and hope, but The Housekeeper and the Professor's unprepossessing tone reveals strong self-definition.  Sure, it's an emotive tear-jerker, but it achieves that end, not by manipulating readers, but by making its characters human and treating us with respect.
When others gave into the rise of central power, Cicero stood fast for the righteousness of the Republic.  He believed that language held the key not only to political goals—his rapid rise in the Roman Senate dropped many jaws—but he also believed that the great rhetorician must first be a great philosopher.  De Oratore, a heavily fictionalized Socratic dialogue, delineates his principles of the wise, well-spoken ideal who would govern the perfected Republic.  This new translation reveals his goals as not only very current, but remarkably lucid, too.
Dr. Asimov was a writer's writer, famously stationed at his typewriter from 6 a.m. to noon, seven days a week.  This rigorous schedule let him produce nearly five hundred books in nearly every genre, including science fiction, mystery, fantasy, history, physics, chemistry, mathematics, and interpretation of Shakespeare and the Bible.  His voracious curiosity, encyclopedic knowledge, and religious work habits made him the ultimate go-to writer for many years.  Selecting just one definitive work would overwhelm even the most devoted scholar-fan, but Foundation makes a good starting point.