Can someone guide me as to what Single driver ??

I am interested in single driver speakers as I have owned 30 pairs of the major brands over the last 20 years, and have gone through upgrade fever over and over. I have been reading good things about SD with set amps which I own, I would only like to spend < 1500$ if posible ALso, can you add a top loading super tweeter to the binding posts to boost the highs?? recommedations? Seems to be a cult thing.