Re:
When I built up my Orange Prestige in 1994 I used a Dia-Compe Ahead set, when I rebuilt the bike the other year I found another Dia-Compe Ahead set for it.
As mentioned above, the Campagnolo headset is another contender, looks classy, pricey but very very good. I've had one on a previous MTB and tbh that headset would probably last the lifetime of the frame!