I've got a CygoLight NiteRider or some such thing. It's handy, rechargeable, and lets me see my way if I end up on a MUP away from city lights, too. But, as I found out yesterday, it can also die very suddenly, leaving me a couple of miles from home on the darkest part of my commute (still in the city, so still not very dark, but it is the point at which I click on the 2nd light). I may need a back up battery light to keep in my trunk. Long term plan is to go with a dynamo so that batteries aren't a concern. I did pass two stealth riders at a particularly dark intersection on a relatively high traffic road. Hopefully they go for some lights some time soon.