My ideal headlamp would have 2 or 3 levels of brightness, regulated so that it would not grow dimmer as the batteries aged. It would be powered by 3 AAA batteries, as are most of the LED standard headlamps I've seen. It would also have a battery indicator to show me how much life is left in the batteries. And of course ideally it would be no heavier than the current Princeton Tech Aurora I'm using.

Solar powered would be very nice but I haven't seen anything like that around yet that is all that bright. Perhaps solar with battery backup?