Night riding is something to experience and it does depend on the type of riding you are doing. The link on the lights below is mainly for offroading and are powerfull lights.
So street riding with street lights and you want to be seen. Best is a flashing LED in excess of 1 watt. This may not be legal and you will have to carry a Main lamp that will throw a beam so that if the lights are not that good- you can see into the shadows.
Then for riding with no street lights and a lamp of around 20w is quite sufficient. Better if it is a Twin 10 watt so you have two beams. Then There are The $$$$'s HID lamps. Only problem with these is they are so bright that oncoming cars have a problem.
I actually use a twin 5w Luxeon LED lamp and this is just about good enough for speed offroad and is completely powerfull enough for onroad.
You have to have a lamp on the bike to be legal- but by far the best lamp you can have is a Helmet lamp. Come in all types- powers and prices but mine has a 3 level LED for seeing the controls- Reading a map or Repairing the bike and a High power spot lamp that is good for 50 yards.
Then you start talking about the battery life- and where to stow it and what type of battery So a simple question about lighting should have a forum on its own.
I personally have the Use Exposure Enduro Turbo- but be warned- this is not cheap either.
http://www.use1.com/exposure/dealers...eb_dealers.php
Link to some Very Good but expensive lights
http://www.mtbr.com/spotlight/lightshootout/