The New Roget's Thesaurus in Dictionary Form is the most authoritative, efficient and thorough reference work on words that you could possess. And this edition contains thousands of new words, including colloquialisms, slang, and scientific terms. Each listing of a word contains synonyms which define it, and a cross reference to at least one other word. If you have ever racked your brains for a better word, a different word, an antonym, or a vivid descriptive phrase, you will find this book indispensable.
How can you not like a book that does nothing more than relate one word to another? The thesaurus is a work of art. It's not like a dictionary which lays out definitions, but more like a map of meaning.
An indispensable reference work, that hasn't been displaced by any other. The internet is certainly quicker, but I can't seem to part with my old reliable.