Here is a wired, dynamo powered taillight that can be mounted right to your seat post or rear seat stay.
The Secula Plus taillight is very bright, projects over a wide area, and presents a relatively large surface of light for an approaching driver to see. No flashing mode! (hooray!)
Compatible with most dynamo systems. Incorporates a stand light so that when the bike comes to a stop the light remains on for a short time.