I can't recommend the Planet Bike Superflash highly enough. Nashbar runs them on sale for $25 on a regular basis. I've used two of them every day for going on 5 months now, and all I've had to do is change the batteries once. I've heard good things about the Cateye LD-1000, but I like the Superflash. The ultimate rear light is the DiNotte tail light, but it's way expensive.