Bar end lights / blinkers
I just bought bar end lights to enhance my night riding visibility. I saw these when I rode with a friend who has a set during one night ride. I was amazed at the complete profile of the bike can be seen even from afar. It's like navigational lights for boats. Drivers can see exactly where the bike's handlebar ends.
They are about $4-10 a pair. I bought 2 pairs for my two bikes unfortunately, it doesn't fit my Giant stock handlebar. It fits the other one easily though.