I think obtaining and delivering a nuclear weapon would be beyond most terrorist organisations.....and why would they want to, when economic terrorism is so easy.
Personally I think the next move will be Smallpox or similar infection delivered by two or three travelling terrorists.
Subways, airports, cruise ships, office buildings.

It is so simple, cant understand why these madmen haven't tried already.   As I have said, terrorism is not a laughing matter, or a matter to be treated lightly.