The Negroni

This is Daniele's favorite drink. I'll be fixing these tonight!

Negroni-Traditional Recipe
1 part Gin
1 part Sweet Vermouth (classically, Cinzano Rosso)
1 part Campari
Traditionally, it would be served on the rocks (and stirred gently), but it can also be served in a cocktail glass after shaking with ice. The traditional garnish would be a slice of orange or an orange twist (you could even flame it if you wanted).

Brief History
Legend has it that the Negroni was named for Count Negroni, who often ordered it at a bar in Italy, initially as an Americano with gin added. The Americans were already loving the Americano drink, so they also adopted the Negroni and some brought it home with them. The drink is intended as a pre-dinner drink, an aperitif, to stimulate the appetite.
Drink Tinkering
You have a choice in gin, and vermouth, and those will affect the final drink. Sweet vermouths can vary quite a lot in flavor, spice and sweetness, so the balance with the Campari can vary quite a bit. You could also adjust the proportions, (sometimes the Campari is just a bit too much for me in the original proportions, so I'll tone it down just a bit, or I might add a dash extra).
And, if you are OK with bucking tradition, you could substitute another spirit for the Campari.

Here is another favorite version:

1 part Gin (he was using our Distiller's Gin No. 6, but it also works with other gins)
1 part Vya Sweet Vermouth
1 part Aperol
Served up, and garnished with an orange twist.
The Aperol is a bitter, but not as bitter as Campari, and its flavor profile is a bit different (sweet orange rather than spice). It blends particularly nicely with the Vya sweet vermouth - I have consistently been impressed with the combination. It has a lovely balance of flavors, each making itself known, rather than one dominating the drink.