Dynamo hub, and probably a B&M cyo for the light. Unless exposure have built their fancy really good dynamo light yet, which will be way better (although that'll blow your budget I guess).
No charging, next to no extra weight in my case (couple of hundred grams on the hub, but the light units weigh significantly less than a battery light - especially one with enough batteries for a regular 30 mile commute), always attached, bright enough for road riding. Brilliant for unexpected late nights in summer. The b+m ones even have a light sensor so they magically come on when you go through a tunnel, or when it gets dark because there's a storm. Oh and you can wire in a rear light too, which auto-switches along with the front light.
I wouldn't have anything else for commuting - particularly for a long commute. The b+m lights are not as bright as the fancy mountain biking lights, but are very well set up for road riding to put the light in the right place, and I'm happy enough riding unlit roads with mine. And did I mention that you never have to charge them.
Basically, I fitted my dynamo lights about 3 or 4 years ago. Turned the switch to 'auto'. Since then, I've ridden thousands of miles, and have never considered lights, they're just there when I need them, and off when I don't.
Oh, and drag, the drag is basically zero when they're off and extremely small when they are on, I can't notice when they turn on or off at all without looking at the lights.