Here's a tip I recently came across: reflective tape.
The other day a coworker almost accidentally side-swiped me because she couldn't see me from the side. At $2 per 30in. roll, reflective tape isn't cheap, but it's effective. I cut it into thin strips on put it all over my frame, fork and rear rack. For those of you queasy about mucking up your frame, I should add that my commuter was built up from a beater and I don't give two squats about its looks.
I had the lady friend help me test the new visibility, and I glow whenever light hits the frame. Just a thought.