Here's my short list.
Guzzi V7 Stone
Triumph Thruxton or Speedmaster
It's really hard for me to pick. I have a 919 now and it's so perfect that any bike I choose will be lacking in some area. There's no clear upgrade.
But it does sort of lack character and it's not a twin. My perfect bike has to be a single or a twin.
The Triumph "Street Tracker" thread is very interesting too.