Some light manufacturers, including Bontrager, Blackburn, Cygolite, Light & Motion and NiteRider, offer head/tail light combinations. Those are all good.
For the headlight, get a minimum of 300 lumens. Up to a certain point, more is better. I need only 300-500 to see well, but having a more powerful light lets me run it at low or medium and get more runtime per battery charge.