Expensive, but well worth it.
I built up new wheels for my tourer with a Supernova hub-dynamo. I have dynamo lights that run off of it as well as a Supernova Plug. It sits where your stem-cap is and it is essentially just a USB port! You can plug anything you like into it and it just charges as you pedal, using power that you generate.
The drag is virtually nonexistant. Equivelant to having about 10psi less in your tyres. Un-noticeable. You have to be doing about 7mph in order to have both the lights on and be charging... Not hard at all.
It isn't the cheapest route to go down, but well worth it if you can afford!
Just my two cents... My friend is bringing a battery pack that can be charged from the mains as well as from a small solar pannel, works pretty well so that is also an option and much much much cheaper! I just like my gadgets.