AAA's really annoy me. Unless the device is really small, no reason not to go with AA's. They hold 3X as much energy for only being a little bigger, and only slightly more expensive too. 2 or 3 years ago I got a Portland Design Works Danger Zone tail light. I'd be surprised that there isn't something much better now, but it seems very bright, with a just wide enough beam to work well on country roads around here. I actually bought it for running, and clip it on my headlamp's band on the back of my head. I was wearing it one day that was very overcast, and an old fella driving a truck slowed down as he went by and actually complimented me saying that it really helped him notice me. Thought that was pretty cool. Only wish it took AA since I've got a bunch of them.

I'm a big fan of Zebralights and have 3 AA headlamps and one 18650 headlamp of theirs. Fantastic lights, and while the beam isnt ideal for biking I find the 18650 powered headlamp to be plenty bright enough. I thought about their red headlamp, and using it as a bike tailight with a TwoFish Block, but it's a lot of money just for that (I wouldn't use red for much else really). 100 lumen on max, strobe mode. H502r Red AA Flood Headlamp it is an open emitter floodlight with no reflector, so a very wide even beam but no focused bright center. Even at 100 l I'm not sure if it would be really bright enough being a true floodlight.