For a AA light, this will get it done:
http://www.amazon.com/Planet-Bike-Bl...planet+bike+2w
I have this light; however, these days I only use it on my road bike if I think I'll be out late. As mentioned above, I have a cygolight 800 that is now my main light. Might be a little more than you want to spend, but they have lower lumen lights that will work very well for road riding. I went with this one:
http://www.amazon.com/Cygolite-Expil...words=cygolite
It has been great.