While there are plenty that are VERY good, almost all I've seen are plenty good enough for what you're talking about. Just get one from a reputable manufacturer (planet bike, cateye, nite rider, etc. -- mostly because you'll be sure to get decent mounting hardware) from your LBS or lump it in with your Amazon order and you'll be good to go for at or under $10. If you're deciding between any two go with the one that can either mount on your seatpost or switch for a clip that allows you to put on your clothing or a bag -- they're really versatile that way for future use (walking, commuting at night, whatever!) Oh, and get one that takes normal batteries, don't mess around with off-size deals. Hey, Amazon's got the NiteRider TL 5.0 for under $7.19. I'd jump on that...