Some good recipes for Oreo fluff are Oreo fluff salad from AllRecipes.com and Kraft's Oreo fluff. Both recipes call for Oreos, whipped topping, milk and vanilla pudding mix.
To make Oreo fluff salad, combine 4 cups of milk with 2 3.4-ounce packages of instant vanilla pudding mix in a large bowl. Once the pudding sets up, mix in 2 8-ounce containers of whipped topping. Crush 30 Oreo cookies in a zippered plastic bag with a rolling pin until the cookies are the desired size, and then fold them into the cream mixture. Spread plastic wrap over the bowl, and chill the salad for one more hour. Serve the fluff once it has thickened sufficiently.
An even simpler recipe uses only Oreo cookies and whipped topping. Chop 16 or 2 cups or Oreo cookies into coarse chunks. Add them to a bowl along with 2 cups of thawed whipped topping. Carefully fold the two ingredients together. Cover the bowl with a lid or plastic wrap, and chill the fluff between two and 24 hours before serving. Another recipe uses 2 boxes of cookies 'n cream pudding mix along with 2 cups of buttermilk, Oreos and whipped topping. Blend all the ingredients together, chill, and then serve.