I run at least two forward lights. I run a L&M Stella 150 on the bar and an old BLT 10W Halogen on the helmet. I find that both lights are ok on their own but not so much in places were it is pitch dark. I discovered that rather abruptly on a dark rainy trail when I nearly ran down a hiker when I was using the BLT on its own. Good thing I was only doing about 20 km/h at the time. I also found the helmet light to be hard on my neck as I had to keep it trained at a particular place.
When combined, the amber glow of the BLT gives off plenty of ambient light and the Stella stark white precise light complements it nicely by focusing on the road. I also keep a cheap 3 LED Cat Eye on the bar as a backup. Aft, I run a Planet Bike Super Flash.