side visibility
My route crosses many short sidestreets, and nearly all my close-calls (even in daylight) have involved inattentive drivers crossing my path. Now that it's dark for the ride home, I've put little red valve-cap lights on my tires. Viewed from the side, they look like two circles of red. Following a suggestion here, I also put Christmas lights the length of my frame; looks goofy and fun, besides adding visibility.