Gin, fresh lemon, simple syrup, and club soda — the template for every fizz cocktail ever made.
The Gin Fizz is the parent cocktail of an entire drink family. Add egg white and it becomes a Silver Fizz. Add both egg white and yolk for a Golden Fizz. Add cream, orange flower water, and lemon for a Ramos Gin Fizz (and shake for 12 minutes). Add egg white and stout beer for a Chicago Fizz. Every variation is a Gin Fizz with something added.
The Ramos Gin Fizz deserves special mention: created by Henry Charles Ramos in New Orleans in 1888, it adds ½ oz heavy cream, 1 egg white, 3 drops of orange flower water, and lime juice to the standard recipe, shaken for a legendary 12 minutes. It's a workout, a spectacle, and worth every second.
Add 1 egg white to the shaker before the ice. Dry shake first (without ice) for 15 seconds, then add ice and shake again. Creates a dense, creamy foam.
Replace simple syrup with elderflower liqueur. Add a sprig of fresh mint to the glass. Floral and spring-like.
Replace gin with sloe gin (or use half each). The berry-almond character of sloe gin makes a dramatically different, fruitier fizz.