My favourite rear light for the past year has been the Planet Bike Superflash. It isn't the brightest red blinkie available, but it's a great combination of inexpensive and effective. I find the strobe mode is ideal for getting driver's attention as it resembles an emerency vehicle flashing light. I couldn't get the mount around the massive seatpot on the Street so I mounted the light to the left side seatstay. If I'm doing a lot of night riding with the Street I'll mount another Superflash on the right seatstay for maximum visibility.