Also consider that if you are serious about riding at night, it is good to have a second, backup light both front and rear in case your primary light fails. A helmet light (e.g. Fenix LD20 Premium, the Terralux mentioned above, some of the Shining Beam lights, etc.) is a very nice backup, helpful in nighttime on the road repairs, you can see ahead into corners, and lets you "awaken" distracted/inattentive motorists. While you can find somewhat cheaper flashlights on Deal Extreme, the ones mentioned have a reputation for better quality & durability. For the rear, you could do worse than two Planet Bike Superflashes or Radbot 1000's. (or one of each for more variety in flashing patterns).

You will probably want to use rechargeable NiMH or LiIon batteries depending on what light setup you go with. Thomas Distributing or BatterySpace are two good sources for the batteries, the LaCrosse or MAHA chargers are popular and sometimes come bundled with batteries.