For no particular reason, the second entry in my list of favorite cocktails is the Sidecar. If you read my first post, it may occur to you that a Sidecar is not technically a cocktail; it's a sour. A sour is merely a spirit plus lemon or lime juice plus a sweetener. That sweetener can be sugar, a syrup, or a liqueur. In lesser bars or in the premade-margarita-mix aisle of your grocery store, you can buy "Sour mix." Skip that, and take the time to make a crisper, cleaner sour mix as it was originally intended: equal parts lemon or lime juice and simple syrup.
This is a very popular family of mixed drinks with hundreds of variations. Consider:
whiskey + lemon juice + syrup = whiskey sour
gin + lemon juice + maraschino liqueur = Aviation
light rum + lime juice + syrup = Daiquiri
cachaça + lime juice + sugar = caipirinha
tequila + lime juice + orange liqueur (eg. triple sec) = margarita
applejack + lemon juice + grenadine = Jack Rose
etc.
