Leeks
These members of the onion family look like giant scallions, and are every bit as healthful and flavorful as their better-known cousins. They come as close to calorie-free as it gets at a mere 32 calories per cooked cup.
You can poach or broil halved leeks and then marinate them in vinaigrette or season with Romano cheese, fine mustard or herbs. They also make a good soup.