Classic Potato Salad

Source: About.com

1 cup mayonnaise 
2 tablespoons vinegar 
1 1/2 teaspoons salt 
1 teaspoon sugar 
5 to 5 med. potatoes, peeled, cubed, cooked 
1 cup sliced celery 
1/2 cup chopped onion 
3 eggs, hard-boiled 
1 to 2 Tbs chopped green onions, optional garnish 
1 tomato, cut in wedges, optional garnish 
Combine mayonnaise, vinegar, salt, sugar, and pepper in a large bowl. Add remaining ingredients; toss gently to combine well. Cover; chill for 2 or more hours for best flavor. Garnish with chopped green onion and tomato wedges if desired.
Serves 6 to 8.