What are the common idioms for the drop portion of a drag and drop operation?

I'm only concerned here with the other half of a D%D operation, the drop. What are the common idioms to communicate to a user they can drop? And which are the "best" and in what situations?

In particular I would like to know ones that communicate something to the user both before the drag occurs and after the drag occurs. These can be visual or 'tactile' (mouse cursor changes).