Perhaps you could on the one hand list books that are quite essential and then on the other hand those that support the campaign well but aren't necessarily needed.
I guess it would probably be a good buy to get "Underdark" wouldn't it, as it should detail the Drow. Or what books would you suggest to get one without too much knowledge of modern day fantasy (apart from Lord of the Rings stuff) into the picture?
And no: I didn't read any books about that Drizzt guy
