With winter coming, most of my runs are getting moved into the dark so I decided I needed to get some gear to help me be more visible. My runs are usually in pretty low traffic areas so after browsing the selection at a sporting goods store, I settled on a couple of these LED lights from Highgear.
They come in red, yellow and green. I chose red and green because they seemed the brightest in the store. They're pretty lightweight (18g each) and have a good grippy clip that is somewhat reminiscent of a medieval torture device. I clip them to my sock and don't even notice they're on when I'm out running. When it gets cold enough, I'll probably clip one to my Barcamp hat.
Three really bright LEDs can be set to light up in three different patterns with a click of the button in the middle. When I look behind as I'm running, I can see road being partly lit up by the light. Should be more than bright enough to attract the attention of anybody coming up behind me.