Cook the ground beef in a large skillet over medium-high heat for 5 to 7 minutes or until thoroughly cooked and no longer pink in the center, stirring frequently. Stir in the tomatoes, beans, chili powder, cumin, salt and pepper. Cover and simmer over low heat for 25 minutes or until thickened, stirring occasionally. Serve chili over a bed of corn chips. Top each serving with the cheese and onion. Dollop with the sour cream and serve.