the CM400's have a real low seat and keep up with traffic just fine. the KTM 390 duke, a little (lot) more expensive but its a hell of a bike and very petite, you could probably lower it an inch or two pretty easy the way the suspension is set up
even the 690's aren't too tall but the 390 is a great size and probably the best starter bike on the market right now. the torquey single cylinder is super forgiving and a blast to ride.
speaking of blast, i've been seeing buell blasts coming up cheap too lately. they can hold highway speed just fine and are pretty petite.