One bar ingredient that I always have on hand is a bottle of Stirrings Blood Orange Bitters.
They are that good combination of sweet and bitter, and add a special touch to a Manhattan or a champagne cocktail. The bottle is larger than most standard bitters (12 oz.) and lasts for a long time. They have more recipes on their site including Americana and Cherry Blossom. I'm most certain that you, dear Cocktailian, can find more delicious ways to use this fine elixir.
Photo credit: Stirrings