Easy, that would have to be the big bubblicious booty of Ki Toy Johnson. You may know her from the Big Boi video "I Like The Way You Move".
She's all natural too....well her ass is anyway. She starred in a video entitled "The Naked Truth" and her boobs were smaller in that movie than they are now. But she says she's all real. You can find "The Naked Truth" at your local Blockbuster Video.