In a medium to large bowl, Combine sour cream,mayonnaise and cumin.Stir well.Add corn,cheese,chiles,black pepper,and onions to the sour cream mixture.Stir with a wooden spoon (are whatever you have) til all is combined.Cover and chill for 2 hours or overnight.(overnight is what I do, the seasonings are blended in better) Serve with warm tortilla chips.