Trim fat from steak; cut steak into 1-inch cubes. Remove and discard husks and silks from corn; cut corn into 1-inch pieces. Combine barbecue sauce, beer, and garlic in a heavy-duty, zip-top plastic bag. Add meat and corn; seal bag, and shake until meat and corn are well coated. Marinate in refrigerator up to 8 hours, turning occasionally.
Cook potato in boiling water to cover in a medium saucepan 12 to 15 minutes or until tender; drain.
Remove meat and corn from marinade, reserving marinade. Place marinade in a small saucepan; bring to a boil. Remove from heat, and set aside.
Thread meat, corn, and potato alternately onto 6 (15-inch) metal skewers. Coat grill rack with vegetable cooking spray; place on grill over medium-hot coals (350° to 400°). Place kabobs on rack; grill, covered, 10 minutes or until meat is done, turning and basting often with reserved marinade. Add cherry tomatoes to skewers during last 2 minutes of cooking time.