I like helmet mounts for seeing the road and don't mind spending my money there. The angle from the helmet is better for spotting potholes and the like and I can aim the light quickly by moving my head. I've been using a 4Sevens Quark with a twofish lockblock for the past several years, but I long for a Zebralight H600w. I run it with a steady beam and angle it down to the pavement about 15-20 feet ahead of me. So far, no complaints from drivers.
The only real drawback to a helmet mount is fog and snow. It can be blinding if the fog/snow is thick. I suppose another drawback is that weight and size is important since it's on your head.
I also mount a handlebar light set on slow flash to catch drivers' attention. Literally anything will do, and since weight doesn't matter much, it doesn't have to be expensive. I'm using a Nextorch mytorch because I wanted to play with it and anything brighter would tick off the oncoming traffic. They can see my cheep-o light just fine.
I know I'm in the minority, but I would only go with a light and battery pack connected by a wire as a last resort. My experience is that the damn wire always breaks (and at the most inconvenient time). The only reliable corded light I've had was one I fixed with a coiled guitar wire from Radioshack. I only need about 90 minutes of light for my commute, so carrying around some hurking battery doesn't make sense anyway. I simply recharge the batteries every night.
Oh, and I didn't point out a couple of the benefits of biking with two lights: 1) I always have a spare if one breaks or the battery dies and 2) cars seem to have a better idea of how quickly they approach me as the apparent distance between the lights gets wider (think about when you approach a motorcycle compared to a car)