I don't have any info on a book or link with special focus on garnishes, but
here's my two cents on the subject:
Garnishes, in most instances, are simply there for visual purposes. 9 times
out of 10 the garnish just gets thrown away. It's true, however, that with
some drinks, the garnish does add more than just eye candy, it also adds
flavor. I have a feeling you already know the more common drinks where this
occurs: Margarita (Lime), Daquiri (Lime, or Lime flag), Bloody Mary (lemon or
lime, celery stalk, salt rim and sometimes olives, dilly beans etc), Martini
(Olive or lemon twist) Manhattan and Rob Roys (cherry), Long Island (lemon).
The rest, I usually go by this rule of thumb: The prominent flavor profile
dictates the fruit to be used for garnish, if OJ is the main mixer, an orange,
or orange flag would be suitable. All Sours and drinks with Amaretto get a
cherry. Anything tropical gets an umbrella flag. And sometimes there are no
special tricks for figuring it out, you just need to remember what the recipe
says =)
Hope this helps.
Cheers!
Josh[at]MostOrdered.com