Doug has his own review of battery-powered signaling devices at
http://www.equipped.org/signal.htm#BatteryPoweredAttraction, which details the emergency strobes (e.g. ACR Electronics FireFly series) and the Greatland Rescue Laser Flares. Add in your flashlights, chemical-luminescent lightsticks, and pyrotechnic flares, and that about covers your nighttime visual signaling options.
If anyone knows of something I missed, pipe up.