In a large mixing bowl, combine the Rice Krispies cereal, peanut butter, powdered sugar, and melted butter. Stir until the mixture is well-combined and sticky.
Scoop tablespoon-sized portions and roll them into balls. Place them on a parchment-lined baking sheet.
Chill the balls in the refrigerator for 30 minutes to firm up.
Melt the chocolate chips and dip each ball into the melted chocolate, using a fork to coat them evenly. Let the excess chocolate drip off.
Decorate with sprinkles or crushed peanuts if desired, while the chocolate is still wet.
Refrigerate for another 30 minutes, or until the chocolate sets.
Serve chilled or at room temperature.