Tangy spices have a sharp and acidic taste, that pinches the sinuses and pucker the mouth. One of the five basic tastes, sourness serves as a warning that food might have gone bad or be harmful. Adding sourness to food will balance spicy and sweetness. It's really good if you want to cut through rich foods, especially ones that are high in fat.
Some sour spices include Ginger and Kaffir Lime.