In a large microwave-safe bowl, mix sugar, butter, water, and corn syrup. Microwave on high for 4 minutes, stirring every 1-2 minutes. Heat 6 minutes longer or until thickened and amber in color. Add vanilla extract and stir well. Pour mixture into a 9x13 inch pan. Spread chocolate chips over the hot toffee. Sprinkle the top with chopped nuts.