Those rubber band style lights absolutely stink. Lots of people here in NYC have them, and they can barely be seen until you're right behind them. Avoid.

If you just want some small lights so people can see you, I like the Blackburn Flea set. Easy to remove and take with you, rechargable, and fairly bright for what they are. These are priced all over the place, so shop around to get the best deal.

A better rear light at only a bit more cost is the Cygolite Hotshot. These babies are BRIGHT.