Book on Bartending
The first three are musts.I recommend them in this order because the first two give different types of background education you will find invaluable.
Gary Regan's Joy of Mixology
Dale Degroff's The Craft of the Cocktail
The Savoy Cocktail Book
Ted Haigh's Vintage Spirits & Forgotten Cocktails (much smaller book with very specific recipes.)
Those will send you where you want to go, namely the golden age of cocktails from 1800-1920.
After that you may want to get the series Mixologist: The Journal of the American Cocktail.