Your desire for disc brakes probably makes the Vaya the most obvious (non-custom/really expensive) choice, though technically speaking, it's meant for off-road touring...hence the reason why it feels a lot like a mountain bike. The only other bike that comes to mind is the Kona Sutra, but I think it has a longer top tube than you're looking for.
2009 BMC Road Racer SL 01 / Specialized Ruby 155
2007 LeMond Reno / Luna Chix Team Saddle
1980-something Lotus Odyssey / Brooks Finesse
1992 Bridgestone RB-2 / Brooks B-17 Imperial
Nada Bike singlespeed / Brooks Team Pro in white