In medium skillet, cook ground beef, corn and onions over medium-high heat until beef is thoroughly cooked, stirring frequently. Drain. Stir in chili powder, salt and cumin. Cook 1 minute.
Spray large skillet with nonstick cooking spray. Heat over medium heat until hot. Place 1 tortilla in skillet. Layer tortilla with 1/3 cup cheese and 1/4 of beef mixture. Fold tortilla over. Cook over medium heat for 2 minutes. Carefully turn quesadilla; cook an additional 2 minutes.
Repeat with remaining tortillas and filling. Cut each quesadilla into wedges. Serve quesadillas with salsa and sour cream.