WordNet sense 1 (overcome as with astonishment or disbelief):

daze, bedaze

WordNet sense 2 (surprise greatly; knock someone's socks off):

floor, shock, ball over, blow out of the water, take aback

WordNet sense 3 (hit something or somebody as if with a sandbag):

sandbag

WordNet sense 4 (make senseless or dizzy by or as if by a blow):

stupefy