St. Germain is an acclaimed elderflower liqueur invented by Robert Cooper in 2007, with a subtle, sweet, and beautifully floral profile. It goes well with so many different ingredients and has become so ubiquitous in recent years that it's earned the nickname "bartender's ketchup."
Though it was introduced in the late 2000s, the bottle harkens back to French art nouveau, with its filigreed label and stately, arcing lines. St. Germain may be one of the best-reviewed new liqueurs in recent memory, but it's also one of the best looking. However, you don't want to keep it on your shelf forever unless it's empty—St. Germain doesn't use any preservatives, so it should be finished within six months of opening.