I rode a season with (
http://www.jetlites.com/) JET Starfire dual beam. They're a bar mounted, dual halogen beam system, NiMH battery with 5 way switch that provides 6W, 9W, 12W 20W and 32W of light. I do both fire road and singletrack and they're fine. You can easily get a few hours out of a charge. They cost about $250.
I've seen HID helmet mounts for $270 (Nightrider Storm) at
www.pricepoint.com. In general, HIDs are more efficient than halogens. I've read claims of 10W HID = 40W halogen. HIDs are obnoxiously bright to oncoming riders, but ideal for the rider behind the light.
One company makes a dual beam light, one HID and one halogen bulb.
Also, consider the pros and cons of bar and helmet mounted lights.
Night riding is a real blast. Old trails become new again. Plus the imagination runs wild out there!