Chives have a mild onion flavor and make a nice garnish.
White onions often have a sharp flavor; smaller varieties include pearl onions, about 1/2 inch in diameter, and boiling onions, 7/8 to 11/2 inches in diameter.
Leeks have a mellow onion flavor and can be used interchangeably with onions.
Shallots have a mild, delicate flavor that is outstanding when added to sauces.
Green onions also are known as scallions and usually have a mildly pungent flavor.
Red onions generally have a sharp flavor. They are valued for their color when served raw.
Yellow onions can be round or flattened; sweet varieties include Vidalia, Walla Walla, and Maui, which are great for caramelizing.
Garlic is strongly scented and pungent. Elephant garlic is larger, milder, and more closely related to a leek.