The Highly Selective Thesaurus for the Extraordinarily Literate
If you're serious about writing and speaking language that crackles with delightful and obscure words, then you must have this book. As indicated by the title, it is a selective thesaurus containing 50,000 words and phrases,   focusing on the more arcane or colorful choices. The main weakness is lack of cross-referencing, but it is nonetheless a superlative supplement to standard thesauri or synonym dictionaries.