Clicking the "Insert" dropdown in the upper-right will let you choose from any fields that are "in play" in the viz, i.e., fields that are on one of the shelves. If the field you want to display is not on one of the shelves, drag it to Level of Detail (but make sure doing so doesn't change your viz, because if the field is at a lower grain than the rest of the fields on your viz, it will). Or wasn't that your question?
My question has a slight twist. I'd like to provide a drop down menu so that the user can pick values in the dimension. For example if I have a dimension called ACCOUNT # and the user sees that one of the account # is wrong, they'd be able to start an annotation and view a menu of options with all values in ACCOUNT #s. That way they can pick the correct account # within the annotation screen.
Currently it seems that Tableau only inserts the current account #. Hopefully this makes sense.
That sure would be cool, but I'm not aware of that functionality. Hopefully someone else can help.
This would be a good one to add to the Ideas section with your use case!