Well, let's start with the title. A crucible is "a container of metal or refractory material employed for heating substances to high temperatures" or "a severe, searching test or trial" (according to dictionary.com, attached below). How's that for a symbol of what happens in this story? Salem has become a receptacle for fiery trials and tribulations. The town is tested, faith is tested, the court is tested, and people are tested.
The gallows is a symbol of justice which has been perverted--in this case justice gone wrong. The court is a symbol of all authority--both civil and moral, in this town. The forest, for all Puritans, was a place of evil and the home of Satan, where only things improper were happening. (By the way, why was Rev. Parris out in the forest the night he saw the girls?!) The poppet which "traps" Elizabeth is symbolic of the ridiculousness and childishness of the town and these proceedings.
Witch hunting, as you mentioned, is the overriding symbol, one which Miller used deliberately as a mirror of the McCarthy era. Almost everything in The Crucible, such as the stones which press Giles Corey to death, can be seen as a symbol of oppression, as well.