Whisk together beer, next 4 ingredients, and 1/4 tsp. each salt and pepper in a small bowl. Pierce steaks several times with a fork. Pour marinade into a large zip-top plastic freezer bag; add steaks. Seal bag, and chill 2 hours, turning occasionally.
Preheat grill to 350° to 400° (medium-high) heat. Remove steaks from marinade, reserving marinade. Sprinkle steaks with remaining 1/2 tsp. salt and 1/4 tsp. pepper.
Grill steaks, covered with grill lid, 5 to 6 minutes on each side or to desired degree of doneness. Remove steaks from grill, and let stand 5 minutes before serving.
Meanwhile, boil reserved marinade in a small saucepan over medium-high heat 4 minutes or until thickened. Serve with grilled steaks. Garnish, if desired.