I've been using a RoyalBlue /o for my nightly rides to and from school. Since it kinda takes me where a downtown business area meets residential neighborhood (Eastside Milwaukee) I don't need a lot of light, just a quick glimps of 50' or so before me. I have a microswitched "trigger" by the brake lever. The RB is a great color for city riding, really turns heads, not too bright for drivers, peds.
Anyway, I use a LM317 adj'ble regulator (radioshack), a pot, resistor and a nicad radio control car battery in the under-seat bag. I mounted the luxeon to a reflector bracket from the seatpost on another bike. On the handlebars, I have full x+y adjustment and the bracket a thumb screw for during the ride adjustments.
The radio control car battery is great, had only to buy a cheap tamiya connector at the hobby shop. Plus, I already have the 15 min charger for the rc car. The battery could be lighter, I guess, but compared to my loaded backpack, its negligible.
Haven't worked anything out for rain, but the lux'll seal up pretty well, I'd imagine.
brendan