I have used _Rodale's Synonym Finder_ for a number of years in preparing lectures and sermons, as well as in writing. A few years ago, I introduced it to a colleague while he was writing a book. His response? "This book saved my life!" This past year, I introduced my [homeschooled] 13-year-old to it in order to give some help with writing a novel. The response? "This book is great, Dad! Thanks for telling me about it!" Needless to add, it is now a necessary part of our writing. I cannot recommend it too highly.
The alphabetical approach makes it extremely easy to use, and removes the step of consulting an index. The [numerous] synonyms are listed alphabetically in categories (e.g., casual/slang); it is difficult to see how Rodale could have made it easier to use--or more useful. I recommend _The Synonym Finder_ most highly it to all of my students, and to anyone who writes.