I've always made the spinach dip on the back of the Knorr's soup box, but this one is nice, too. It has a tangier taste, and I'm more likely to have the ingredients for this at home.
Ingredients:
1 cup mayonnaise
1 cup sour cream
1 (1 ounce) envelope ranch dressing mix
1 (10 ounce) package of chopped spinach, thawed and drained well