I have a sackful of these things: Amazon.com : CREE XML XM-L T6 LED Bike Bicycle Light HeadLight HeadLamp 1200LM Red : Cycling Electronics Accessories : Sports & Outdoors (NB: not that precise seller but as far as I can tell they're all probably coming from the same place anyway)

They're basically magicshine clones. I have the actual magic shine as well, which was more like $80 and it's slightly nicer. The battery pack mounts on the head tube under the stem, or under the top tube right up against the head tube.

They're very bright but I'm pretty sure the lumen rating is some sort of theoretical fairy-dust maximum. I go on 2.5 hour rides during the week and have yet to run out of power (I usually run it on high on streets, and medium if I'm on a path like SART)