Obviously this is just a personal opinion. First off you can credit card or ultra light tour on any bike, but not any bike can do medium touring. If you want to do medium touring look into Cross bikes, their built more stout then a road bike but not quite as much as a full fledged touring bike. Bikes Direct has a pretty good selection of Cross bikes at prices that will beat LBS's; otherwise LBS selections include Kona, KHS, Jamis, Raleigh, and Surly and a few others offer nice cross bikes.

Even a standard road bike can handle light touring, but wouldn't be idea of medium weight. Problem with using road bikes is the geometry is tighter and will be less comfortable on day in and day out riding but people have done it. You can buy special quick release skewers with attachments that a Tubus rear pannier rack can mount to; see item 2: http://www.thetouringstore.com/TUBUS...ONS%20PAGE.htm

As far as compromises with cross bikes...the gearing is not quite as low as a full fledge touring bike, true, but you won't be hauling 65 to 75 pounds either, or a trailer, you'll only be carrying a max of 35 pounds which is fine with cross gears, and if you need better gears you can swap the gears with little problem.