Nobody reads a reference book to be amused, much less charmed. Useful though they are, the vast majority of dictionaries and encyclopedias are poker-faced pieces of work that stick to the facts and present them as soberly—and unstylishly—as possible. One of the reasons why this is so is that such books tend to be written not by individuals but by panels of experts. Try to imagine a joke written by a committee and you’ll get the idea.
Fortunately, there are a handful of shining exceptions to this drab rule, the gaudiest of which is H.L. Mencken’s New Dictionary of Quotations on Historical Principles From Ancient and Modern Sources, a million-word monster (the original manuscript weighed 35 pounds) that is celebrating its 70th birthday this summer [2012]. The “New Dictionary” was a byproduct of its prolific editor’s fanatically industrious journalistic career. For years Mencken maintained a card file of quotations “that, for one reason or another, interested me and seemed worth remembering, but that, also for one reason or another, were not in the existing quotation-books.” In 1932 he decided to turn it into a book. When the “New Dictionary” finally saw print a decade later, Time praised it as “one of the rare books that deserve the well-worn phrase ‘Here at last.'”
Painstakingly organized and cross-referenced by subject, with each entry arranged in chronological order by date of original publication, the “New Dictionary” is formidably wide-ranging. Indeed, the only major writer missing from its index is Mencken himself. (“I thought it would be unseemly to quote myself,” he told a curious reporter. “I leave that to the intelligence of posterity.”) Its 1,347 pages abound with such innocent-sounding rubrics as “Civilization,” “Flag, American,” “Hell,” “Hypocrisy,” “Old and New” and “Science and Religion.” At first glance you might mistake it for a cornucopia of the world’s wisdom—but don’t let appearances fool you. The fathomlessly cynical Mencken wisely warned his readers in the preface that the “New Dictionary” was aimed at “readers whose general tastes and ideas approximate my own…. The Congressman hunting for platitudes to embellish his eulogy upon a fallen colleague will find relatively little to his purpose.” […]
For all its sly wit, H.L. Mencken’s “New Dictionary” is in point of fact a full-fledged reference book, one whose comprehensiveness and logical organization make it wonderfully easy to use. Would that it were still in print, but used copies are easy to find and worth acquiring. Rarely does a week go by that I don’t have occasion to consult the “New Dictionary,” frequently with amusement, usually with profit and invariably with gratitude to its maker, who may have been a cynic but who was also an amateur scholar of the highest seriousness—one with that rarest of scholarly attributes, a sense of humor.

(Via The Wall Street Journal; picture from biblio.com)
I would love for a new edition of this book or a viable ebook. Digital scanned copies can be checked out on archive.org. The drawback is that the scan is dicey in spots. I picked up my dead tree edition off of eBay (or maybe Amazon) in slightly damaged condition originally sourced from the Rowan Public Library of Salisbury, North Carolina.

Martin Amis uses a thesaurus. The British novelist and critic is known as kind of a snob, and the thesaurus is known as a dangerous tool abused by amateur writers trying to sound smart, but as you’ve probably guessed, Amis uses his thesaurus very differently than a college freshman. In the Big Think video […] (via Open Culture), he describes a better way to use a thesaurus. […]
Amis uses a thesaurus to match the style and rhythm of his words. He might find his current word too long or short for the sentence it’s in. Or he might want to avoid an awkward rhyme or alliteration. He points to Vladimir Nabokov, who changed the English title of his novel Invitation to an Execution to Invitation to a Beheading. Say both out loud and you’ll hear the improvement.
He also double-checks his word use by looking up words in the dictionary—not necessarily to check their definitions, but to check their etymology. For example, he says, the lapid in dilapidated comes from the Latin word for stone, so while he might refer to a dilapidated house, he wouldn’t refer to a dilapidated hedge.
You don’t have to be as careful as Amis with your word choice.

(Via Lifehacker: picture Mark Miller)
You should be as careful as Amis. I try to be:

if you truly want to write better, pay more attention to the rhythm of your words, and study their usage and etymology. Your thesaurus and dictionary are one right-click away—use them well.

Check out my Tools page for a listing of mostly free resources for writing, presentation tools, and tips.