I use the Cateye el-500 series, I guess the new ones are EL-540 or something like that. They are hardly the brightest or lightest, but they work well and 4AA batteries last a long time. What's nice is they do a quick tab disconnect and you can carry them like a regular flashlght, that comes in very handy. And they are relatively cheap, like in the $50 range. I use them in pairs. I've done 8 hour night rides with them, no issues.