In a large bowl, stir together the rice cereal, oats, and raisins. Set aside. Grease a 9x13 inch baking dish with cooking spray.
Combine the brown sugar and corn syrup in a small saucepan over medium heat. Heat just until boiling, then remove from heat and stir in peanut butter and vanilla until smooth. Pour over the cereal and oat mixture, and mix well.
Press into the prepared pan using the back of a large spoon. Allow to cool, then cut into squares.