Couple of things. First, I stopped at REI the other day, and they had CygoLite Niterovers on sale for $43, including the NiMH battery. That is a very cheap price for a great light system.

Second, I recently ordered a Fenix 2xAA flashlight, and I cannot believe how bright it is. Although I haven't had a chance to ride with the light yet, I compared it side-by-side with my old CygoLite NiCAD system, and the Fenix is much brighter -- even running in the non-turbo mode. I cannot believe how small and light the Fenix is, and two lights would probably be overkill for my purposes. You could easily carry a couple of extra AA batteries for backup, and it still would be much lighter than most light systems.