I've got a pair of modified Mini Maglites on my bicycle. Here's the stuff I used. There are certainly other ways to do it.Mini Maglite
: Ubiquitous. If you don't have one lying around the house, ask around. Worst case scenario, you can pick one up at a local chain store, or on Amazon or eBay, for less than ten bucks.
: This CNC-machined aluminum bracket is wildly overbuilt, and the second most expensive part of this setup. It's also, by far, the best way to mount a Minimag to a bicycle handlebar. (Dave Garoutte, the DKG in DKG, is a mtb guy from way back in the day. He also makes a clamp for the C-cell Maglites, which I think would be an awesome choice for a beach cruiser, utility bike or vintage mtb, and some very nice seat clamps.)
Terralux Ministar2 Extreme 5-watt LED upgrade (TLE-5EX)
: The most expensive part, this was, at the time I bought it anyway, the highest-output Minimag bulb available (and much, much brighter than the LED Minimags).Nite-Ize IQ Switch
: The extra resistance dims the LEDs incrementally, but allows for flashing and low-med-hi modes. If you don't need those things, you can skip the switch.Minimag mineral glass lens
: Also probably not really necessary, but high-power LEDs can throw off some heat, and, hey, it's a buck-fifty. I got these last three things from Lighthound
. There are other vendors, but Lighthound seemed popular with people on flashlight forums. I have no relationship with them other than 'satisfied customer.'
Once you get all the parts, it's pretty obvious what you do with 'em. This setup is pretty bombproof, completely user-serviceable, and the lights can be easily removed with one Allen wrench. But while it's much brighter than any AA-powered bike light I've ever seen, it's not as bright as most dedicated cycling lights. On the other hand, it's not as expensive either. And it runs off regular AAs, which may be a plus for some folks.