Dahon, Bike Friday, Brompton all seem to be solid folders.
I came close to buying a "breakaway" bike - either by Ritchey (Breakaway) or Dahon (Allegro). These are full side bikes that break apart at the seatpost and close to bottom bracket, and pack up in a large suitecase...
I LOVE my Tom Ritchey Break Away. Ti / Carbon Dura Ace. It is best suited for long trips and not train hopping as it only breaks in half and the big size is kinda a bitch to pack in it's case. You would never know it's a folder riding it.
All my friends I brought here are getting Dahon folders and I have thought about it to go train up to Tokyo. But am waiting to ride theirs first to see if they will fit a guy 6'3. I LOVE the Moulton but don't see it as a train hopper either.
Also you can make any bike [ Steel with round tubes ] a break away. S&S couplings. Unions for your frame. I think it would run you around 200 USD. Adds a bit of weight but your bike will ride the same. You have to go through a certified frame builder who of course is more interested in selling you one of his frames though. I was going to have my Raleigh 29er done but for some stupid reason the frame tubes are slightly oval. Guess it's engineering for engineering's sake. TODO