If you are riding after dark or before dawn (subtle distinction, that) common sense dictates and the law requires that you be lit.
We carry three brands of lights: Cateye for their range and quality of products, Planet Bike for their "Super Flash", and Light & Motion for their quality, service, and their strip-the-paint high-end light. If your goal is to obey the law and you don't mind riding at about a walking pace, you can get by with front and rear 'blinkies'. If you plan on riding at night in any kind of safety at all, we really Really believe you should throw economics to the wind and use the brightest, best light you can find. We believe that the brightest, best light you can find is the Light & Motion Seca 2000. Not only does the 2000 guarantee that you will be seen, its well designed lighting pattern combined with mind boggling illumination guarantees that you will never 'out run' your light and encounter some unexpected, possibly life-altering obstacle.
So. Get lights (no choice there), get the best lights you can and get as much light as you can afford. That is our motto. That and "We will sell no bicycle before someone pays for it".