From Allrecipes: "This is the quickest and easiest appetizer I know of. It takes only minutes to make and can be served almost immediately. You can keep the ingredients on hand for months. Serve with buttery crackers."
Mix the sour cream with ranch dressing mix in a bowl until smoothly combined. Add the cream cheese and Cheddar cheese to the bowl, and mix together with your hands until thoroughly blended. Chill the mixture for 5 minutes, then shape into a ball.
Place the pecans into a shallow bowl, and roll all sides of the cheese ball in the pecans to coat. Serve immediately.