Walmart has these blinkies that are so easy to mount, for $12. I keep a set handy for travel (I like to rent a bike when I travel) and visitors. I've given more than one set away. (One unintentionally to someone who raided my seat pack.) They seem bright enough for city riding which is mostly pretty well lit by street lights. My commuter has lots of lights, generator powered or magnet powered. If you can spend a little more I really like the reelights which are magnet powered, so I never have to worry about a battery running out.