Originally Posted by Giro

Sooner (in a do-it-yourself system) or later (in a commercial bike light) I expect to see the new LED motorcycle headlights or passing lights adapted for bicycles. These offer some very sharp cut-offs and real optics that put the lumens where you want them. In the first composite photo, note how sharp the cut-off is for the JW/HD passing light in the lower half of the photo. In the on road photo, first marker at 20 yards, then every 10 yards:

They are a bit pricy now (although the passing lights are under $200). See this Feb 2011 review, LED Forward Lighting Comparison (the above photos are from this article) and browse over to what the manufacturers they mention have to offer.