In the depths of winter here it gets dark at 4 so I recently got interested in black reflective tape and better lights. As I was at it, I think I paid £2 for a pair of these:


They snap on a spoke, have a light and motion sensor. When it's dark and in motion it flashes, alternating between red and blue leds. Adds some good side visiblity for a couple quid! Go to ebay and search for spoke light.