Silhouette targets, water filled milk jugs/2 liter bottles/laundry detergent containers(I'm partial to TIDE, they are orange), aluminum cans, 12 ga. hulls (w/scope of course) inflated ballons taped to plywood, etc. etc.
Have also used:
25" console TV
30 gallon water heater at 300 yards
empty beer keg
full cans of old hot beer (shaken not stirred)