I think there are lots of good suggestions made here.
Maybe the experience I have had may help.
Avoid a coupled rangefinder folder. These cameras are more than 50 or more years old and while there can be some really amazing examples out there, they are more susceptible to failure and breakage. Adding a coupled rangefinder complicates the entire camera (more to go wrong), adds bulk, weight, and at least another hundred dollars.
A few years ago I sought out a coupled rangefinder folder as well and decided on the Certo Six, which is a fantastic camera with a great lens, but has a ton of quirks.
I do not shoot with it any more because the rangefinder is out of whack and would need to be replaced/rebuilt. All that happened was that I banged into a wall (lightly) and the rangefinder went totally off kilter and the repair man could not completely realign it. I have been thinking about sending it off to a camera repair specialist, but I have a few other folders that suit my needs pretty well and as such it is not high on my list of priorities.
One of which is the Voigtlander Perkeo I with a Prontor shutter and Color-Skopar lens that I managed to pick up for less than $20 and it works really well, even without a CLA. I can not believe how lucky I was.
The Skopar is a Tessar clone, which will probably be the best type of lens you will pick up in one of these cameras, that is if you do not go for the Voigtlander Bessa II with the Heliar or APO-Lanthar which costs a lot of money.
I focus by guessing (which really is not so bad), but you could pick up an external rf to mount on the shoe.
Features:
Cold Shoe
PC x-sync
Single coated Color-Skopar f/3.5
Tripod socket
Double exposure prevention (though I wish I had the ability to turn it off)
Foot (to prop itself evenly on a surface)
Swinging bracket for easy loading
Small size (smallest 6x6 I have seen)
Excellent build quality
The only things that I wish it had:
Off/on switch for double exposure prevention
Shutter speed that went up to 1/500th
Aperture that went down to f/22
If you are interested, check out the links to some pictures I have made with the camera:
http://www.flickr.com/photos/antonandreas/5885929675/in/photostream
http://www.flickr.com/photos/antonandreas/5520164005/in/photostream