Ted Haigh, a.k.a Dr. Cocktail, tells us what we do with the cocktail ingredient: bitters. His book is Vintage Spirits and Forgotten Cocktails. He also writes a regular online column for Martini Republic.
The websites he mentioned are Buffalo Trace, Sazerac.com, Angostura.com , and FeeBrothers.com.
He runs the Internet Cocktail Database a comprehensive encyclopedia of cocktails, barware, and more.
Click here for a recent article in the NY Times about Ted. He created Mixilator: The David Embury Random Cocktail Generator. This automaton creates brand new cocktail recipes using the complex mixing theories of author David Embury and the ingredient database of the Internet Cocktail Database.