If you want to learn some things, and might be willing to spend some money to get a relatively high-end light, I recommend you look over what Peter White Cycles offers:
http://www.peterwhitecycles.com/lightingsystems.htm
I'm saving up for one of these:
http://www.peterwhitecycles.com/b&m.asp
but I already bought a sidewall dynamo from him and I like it A LOT:
http://affordableluxuryblog.com/2010...cle-generator/