Get a flagman's vest, with lots of reflective crud on it. Put reflective tape on your rim, and on your helmet. Bright front light. The more you ride at night, the brighter you'll wish your light was. I finally caved and bought an HID from batteryspace.com; about $200 and worth every penny, though I built a halogen for last year for about $30, and a bright LED such as the cateyes mentioned, or the Planet Bike SuperSpot, can also work well. I've also found a Luxeon-based LED flashlight at WalMart that uses 3 AAA batteries; I zip-tied it to my helmet and it's surprisingly bright; brighter, in fact, than the Planet Bike superspot that's supposed to have the same LED; I think this must be overvoltaging the LED (which works fine, just reduces the lifetime by a few thousand hours).