If you search the bike forum threads for "homemade headlights", you will find some awesome ideas. I did the same and built my system with a small 12volt SLA battery ($35) and a 55watt 12 volt lawn and garden spotlight mr16 bulb ($2.50). I use a 12 volt battery charger to charge it at night ($20). At this point, I feel safer knowing that I am extremely visible.

I had my wife hop on my bike and ride about two blocks away so I could see how it looked from a distance, and was seeing spots for a few minutes afterwards. Bright doesn't even begin to describe it. It's like riding in daylight at 2a.m.