My personal preference is a dynamo system such as the Busch and Muller Dymotec 6. The B&M Dymotech Oval Plus headlight has a bright halogen bulb with a good focused beam plus a decently bright white LED standlight for when you're stopped. In combo with a B&M Dymotec DToplite Plus taillight this setup gives good front and rear visibility and also lights the road in front of you so you can see where you're going. These may be a little hard to find in your LBS; if so, Peter White Cycles is a good source over the internet. The complete B&M setup - dynamo, front and rear lights and dynamo bracket, prices out at just about $100. Bonus - always permanently installed on your bike, and you never need to worry about batteries again!
http://www.peterwhitecycles.com/dymotec.asp