A classic that I have loved for a while is a Negroni. The Negroni is a simple to make cocktail with only three ingredients.
1 oz. Gin (I prefer an dry "London Dry" type Gin for this drink")
1 oz. Campari
1 oz. Sweet Vermouth
This cocktail should be stirred in a mixing glass with ice for approximately 30 seconds to make sure it is nice and cold. Strain into a chilled cocktail glass, or a rocks glass filled with ice.
Bastian Heuser, one of Germany's top mixologists, created the Agavoni, a wonderful drink inspired by the Negroni.
3/4 oz blanco tequila
3/4 oz sweet vermouth - Heuser recommends Carpano Antica
3/4 oz Campari
Grapefruit twist, for garnish
Build in a rocks or old-fashioned glass filled with ice. Stir briefly to mix and to chill; garnish with a grapefruit twist.