as an ex flashlight geek, I'm thinking up of ways to use them for my bike.
You can use one of those inexpensive 1watt luxeon headlamps as a tail or headlight.
the plastic adjusting and battery latch on mine broke and I use a rubber band to hold it together.
It's bright, has 3 levels and flashing mode. mine uses a side emitting LED.
I took a red filter from my GI angle light and it fits right into the lens of the head lamp.

http://batteryjunction.com/f5fx-hlx712l.html


I also bought the one that uses AAA batteries, the LED on that one looked better.