I saw a reference to a dynamo electric charger installed on a rack in the ACA's email-letter. Here is a link to the device: http://cea.mblast.com/ws/wfaward/rsp/votenomination.asp It is a clever idea but I can't see it working that well on a touring bike where the rack is integral to the entire enterprise.
The basic idea is that the dynamo wheel is placed in contact with the rear tire which turns it to generate electricity. Why couldn't the same idea be applied to a pop-down wheel that turned through contact on the road?
My initial thought is for a small rubber wheel that would attach to the down tube just in front of the bottom bracket that could be flipped down onto the road while you were moving to generate power.
The only downside would be for people who put a third bottle cage on the bottom side of the downtube, though I doubt that would be a show stopper.
I'm not electrically nor mechanically inclined but it seems like a straight forward idea for someone who knows about generators and charging electronics.