I like having 2 headlights, with one on helmet as tjspiel said. You can aim a helmet light into turns to illuminate shadows that might be hiding a person or animal (deer are cute but not your friends!) and to get a driver's attention. Some pretty powerful yet small lights have helmet mounts, so it could be your only light or your primary light. #2 could be a self-contained unit - something like Planet Bike's or one of the more powerful Cateyes. To mount it, try tjspiel's plastic pipe suggestion, or get one of the accessory mounts designed to mount a computer or light on aerobars.

Don't stint on taillights. Planet Bike Superflash and the knock-off version Performance & Nashbar sell are quite bright in strobe modes, I have one on the saddlebag and one on the back of my helmet. I also have reflective ankle wraps for dusk/night commutes. Smaller blinkies may not be noticable enough to give an overtaking driver sufficient warning you're out there.