In a mixing bowl, combine flour, sugar, cocoa, soda and salt. Add the water, oil, vinegar and vanilla. Beat on low speed for 1 minute. Beat on medium for 1 minute. Pour into a Pam sprayed 13 x 9 x 2 inch baking pan. Bake at 350 degrees for 40-45 minutes or until a toothpick inserted near the center comes out clean. Cool on a wire rack.
For frosting, in a mixing bowl, beat the milk and pudding mix for 2 minutes. Beat in whipped topping. Spread over cake. Refrigerate leftovers.