I've done a bunch of riding in the dark, primarily early morning. Most of the riding was on a multi-use path. For the portion that is on streets with traffic it was very important to be visible to traffic. Statiscially speaking the odds are pretty good you'll not ever have an incident. That said, I want to be visible.
I made a homebrew light running off a 14.4 volt battery and it was great for illuminating the path in front of me. I'm not a fast rider to begin with but a good light will allow you to ride faster than a bad light or no light. Really, it is all about being able to see the one out of a thousand events with enough time to make them non-events
I did use a helmet light (in addition to the headlight) for a while. Thing with the helmet light is that the light follows your head. I didn't really care for it.
I bought the brightest biggest blinking light (at the time Planet Bike) I could find for the rear. It was a bit pricey, but worth the cost to me.
I also added reflector tape so the outline of the bike will show when headlights hit it. Reflectors on the wheels really jump out because they are moving.
Like I said above, it really depends on where you are doing your riding as to how much light you need. If you are entirely on paths and are not fussed that you will move slower than riding in daylight - your light needs are not the same as in a different situation.