Muffinator,thats kind of a open question. what you need to find out is what kind of lighting you want on you bike? for example if your headlight is a 4 inch seal beam or a standard car bulb. they will draw about 2amp's and if you deside to have a rear tail light that will be another 2 amp's and if you start to look at the small mini generaters i believe most may only put out 2-4amp's total. also do you want a battery on board? maybe a electric start too.
you really need to figure your lighting first and also another option can be led bulds. they draw less then a amp.
i think my project build bike could be a big help. that bike has a dc lighted coil that only put's out 2 amp's and all my lights are led bulbs. so most of the amp's go straight back into the battery. almost like if it was giving it a trickle charge. i can drive for hours and not worry about over charging the battery and still have enough juice for the electric start..:thumbsup:
http://www.oldminibikes.com/forum/project-logs/12275-project-build-rear-springs.html