Perennial Rosmarinus officinalis has many varieties—some better for large pots ('Miss Jessup's Upright'), others for smaller ones ('Blue Boy')—but all varieties offer a piney, pungent, rich, warm flavor that adds zest to berries, citrus, pears, and apples, especially when paired with vodka, sparkling wine, and gin. I love adding it to gin-and-tonics both in syrup form and as a playful stirrer.
Perennial Aloysia triphylla lends a lightly floral, bold citrus flavor to drinks with, say, apricots, peaches, bananas, berries, and tropical fruit; used in fruity cocktails and sangrias, vodka lemonades, or lemon drop martinis.
Perennial Lavandula angustifolia (English lavender) has the fullest, sweetest flavor, with lemon and citrus notes that add verve to lemony drinks (especially limoncello) and sparkling wine when used primarily as a syrup. Garnish a champagne flute with a single flowering stem and wait for the wows to follow.
Cilantro. The grassy, earthy, slightly soapy flavor of annual Coriandrum sativum complements drinks with tomato or tropical fruit bases. Rim a margarita or bloody Mary glass with finely chopped leaves mixed with sea salt and garnish each glass with a few sprigs. Some taste buds are averse to the flavor, so know your audience.
Anethum graveolens offers a slightly sweet, delicately tangy, grassy flavor that commingles excellently with vodka- and gin-based drinks, especially ones with cucumber garnishes. Technically an annual, dill self-seeds generously to become a permanent garden presence. Try it as both a syrup and wispy garnish.
Infusing an herb's flavor into a drink is best done by adding it as a simple syrup or using a muddler—an 8-to-10-inch baseball-bat-shaped tool designed to help gently mash or "bruise" the herbs to release their oil and fragrance. I prefer the look and feel of old-fashioned handmade wooden ones, but newer stainless-steel ones are easier to clean and offer "teeth" at the bottom that allow for some serious mashing—a plus for blending fruit alongside herbs in, say, a mojito. Inevitably, though, this question will arise: Which side to use for muddling—flat or round? The answer is easy to remember: The flat end works best for a flat-bottomed glass (most cocktail glasses) and the round for a round-bottomed glass (think flute or pilsner). In lieu of a muddler (ranging from $2 to $25), a simple bar spoon will work fairly well.
Any cocktail-perfect herb can be made into simple syrup, which adds flavor with ease and speed. Here's how I make my mint syrup: Add about 12 to 14 fresh mint sprigs or a cup of loose leaves to 1 cup sugar and 1 cup water that's come to a boil. Remove the pot from heat, cover it with a lid, and let the syrup cool to room temperature before straining it into a clean container (usually a squeeze bottle) that can be refrigerated for a couple of weeks. The same can be done with other herbs. When working with more delicate-flavored herbs, use twice the amount of leaves to capture as much of the flavor essence as possible.