Liqueurs (also known as Cordials) are sweet, spirits flavored with fruit, herbs, nuts, spices, flowers, or cream and bottled with added sugar.

Amaretto

Amaretto is a liqueur with a distinct flavor of almonds, though it's often made with apricot pits kernels. The original liqueur, Amaretto di Saronno, hails from Saronno, Italy.
24-28% alcohol by volume (abv). 110 kcal*/oz

Baileys' Original Irish Cream Liqueur.

Milky taupe color. Chocolate-covered crushed hazelnuts and almonds aromas with a deft touch of mint and coconut. A rich, satiny entry leads to a plush, moderately sweet medium-full body of toasted coconut, delicate marzipan, mint leaf, and creamy nougat flavors. Finishes effortlessly with roasted walnuts and a breath of whisky. Remarkable texture and smoothness—a classic cream liqueur.
Irish Cream can be drunk by itself, over ice, or as part of a cocktail. It is also commonly used as an addition to coffee in lieu of cream or sugar.
43% Alcohol. 103 kcal*/oz

Bénédictine

Made of herbs, roots (contains 27 plants and spices) and sugar with a Cognac base. Originally used to revive tired Benedictine monks beginning in 1510, the term D.O.M. found on the label stands for Deo Optimo Maximo which translates to "to God, most good, most great" reminds us of the liqueur's origins. One of the best ways to taste the distinct flavors of Benedictine is in a B&B in which the liqueur is mixed with brandy.
43% alcohol.

Crème de cacao

A sweet chocolate liqueur flavored primarily by the cocoa bean and the vanilla orchid. It is normally made as a clear light syrup, however it is also available in a dark caramel-colored syrup, often labeled as "dark crème de cacao."
20-25% alcohol. 100 kcal*/oz

Crème de menthe

A very sweet mint flavored liqueur. It come in two versions, green and white (clear). There is no noticeable flavor difference between the two.

When a recipe calls for creme de menthe, the white variant is usually the correct to use.
Used in the Grasshopper and the Stinger.
25% alcohol.

Drambuie®

A honey and herb-flavoured golden scotch whisky liqueur made from aged malt whisky, heather honey and a secret blend of herbs and spices. The flavour suggests saffron, honey, anise, nutmeg and herbs.
40% alcohol. 105 kcal/oz
See:
wikipedia, Drambuie_recipes

Galliano

Galliano, also known as Liquore Galliano, is a sweet, yellow Italian herbal liqueur. It is flavored with various herbs, flowers and spices, including anise, licorice and vanilla, giving it an unique taste.
30% and 42% alcohol. 100 kcal/oz
galliano.com

Glayva

The smooth and mellow Scotch wkisky liqueur made in Scotland to an ancient recipe using the finest Scotch whiskies, wild heather honey, anise, clove, herbs, tangerine, other citrus fruits, and almonds. and the back label: Glayva is unique -- a blend of the finest selected Scotch whiskies, each chosen for its smoothness, mellowness and maturity, which are then married carefully with a rich variety of natural herbs, honeys and flavourings to achieve the distinctive and original taste which which is its hallmark and which has pleased and attracted so many.
40% alcohol. 103 kcal/oz
glayva.com
* I couldn't find Glayva at any stores. It wasn't in their catalogue either. The only US source I found was Wine Globe.

Grand Marnier

Grand Marnier is a kind of triple sec, made from a blend of true cognacs and distilled essence of bitter orange.
Recipes at grand-Marnier.com

Kahlúa

Mexican coffee-flavored liqueur. It is heavy and sweet, with a distinct taste of coffee, from which it is made. Kahlua also contains sugar, corn syrup, vanilla bean, and Vodka.
Used as a topping or ingredient in several desserts, including ice cream, cakes, and cheesecakes or in White Russian and Black Russian coctails.
26.5% alcohol. 91 kcal*/oz

Peppermint Schnapps

Peppermint Schnapps is a strong, dry spirit based on fresh peppermint leaves.
Serve with lamb, fish, vegetables, soups, desserts, many types of cheese, and cheese cakes.
50% alcohol

Triple sec

Triple sec (meaning "Triple distilled") is a strong, sweet and colorless orange flavored liqueur made frombrandy or Congnac. It is made from the dried peel of oranges found on Curacao, an island in the Caribbean.
In addition to the generic brand Triple Sec, Curaçao, Cointreau, and Grand Marnier are also triple secs.
often paired with Tequila drinks such as Margaritas.
23-30% alcohol. 103 calories

Links:
Liqueur & Cordial Facts
Homemade liqueur recipes: at DrinksMixer.com.
See also: Mixers