I ride with a group that does night rides throughout the year (just started with lights this week), and here's the general wisdom.

LED lights are good for being seen but don't put out enough light to see in the low-power versions. And the high-power versions aren't any more efficient than a halogen light.

Halogens work well - they put out a lot of light.

HID lamps are the best - they put out a ton of light.

And those three are priced in that order. Good lights are in the hundreds, and one of my friends just bought a new top-of-the-line HID lamp for $650.

Some lights give you multiple light levels. You will pay more for that.

For batteries, NiCad are old tech. Either NiMH or Lithium Ion are good batteries - NiMH batteries self-discharge and are heavier, but either work well.

I have a NiteRider that's several years old that works great. It's a 13 watt halogen light.

I'd recommend choosing a system from a company that just makes lights.