Beat Cream Cheese Until Smooth. Gradually Beat In Sugar. Blend In Sour Cream And Vanilla. Fold In Whipped Topping, Blend Well. Stir In Chocolate Chips. Spoon Mixture Into Pie Crust. Chill Pie For 4 Hours Or Until Set. Granish With Whipped Topping, Chocolate Shavings Or Fruit, If Desired.