How much money do you want to spend.
You can start with a Fenix flashlight at about $50 then go up from there to $300 or $400 for other lights.
I have 2 Fenix flashlights mounted on my bike. I like them because they are simple, relatively in expensive and VERY BRIGHT. I owned 3 bike specific headlights before. Each was about $100. Each broke in less than a year. None were as bright as one Fenix.

You can see a lot of light reviews in the Electronics forum. Search for 'headlights'