I found a great solution that seems to be the best of both worlds. Try reelights (www.reelights.com). They are LED blinkies that are powered off magnets mounted on the spokes (no batteries). A pair is about $50, more than a normal set of blinkies but far less than a dynamo hub. They are as bright as a normal rear blinkie, run for at least few minutes after you stop (5-10 minutes when fully charged in my experience, more than enough for stoplights and so forth).The front white light is not bright enough to see where you are going on a dark path, but bright enough for cars to see you.
You don't have to worry about batteries, but you also don't have to pay the high cost of a dynamo hub. If you want a headlight bright enough to see with, you would need a dynamo, but for "be seen" lights, particularly a rear blinkie, the reelights are perfect.