Here's another bottle generator: http://www.velo-orange.com/spdy.html It's a little cheaper than the Busch & Müller linked to from Harris, but probably not as nice.

There are 3 basic types of generators:

1) "bottle" generators that have a roller that goes against the side of the tire. They can be disengaged so they don't touch the tire when not in use, so they have no drag. When in use they tend to have the highest drag when in use. They also tend to wear out the tire sidewall. Maybe it wear out before the tread wears out from riding, maybe it outlasts the tread. YMMV. They also can be difficult to get properly aligned so they get good grip on the tire. They also have a reputation for slipping when wet, which is when you really don't want your lights to get flakey on you. They're the cheapest, and you get what you pay for.

2) roller or "bottom bracket" generators. They mount behind the bottom bracket and have a roller that contacts the center of the tire tread. Completely disengages so there is no drag when you're not using it. I'm not sure how the drag compares to a bottler generator when in use, but I suspect it would be lower. I'm also pretty certain it will be higher than most hub generators. They're pretty rare now days.

3) Hub generator. This is built into a hub for the front wheel, so it requires buying/building a new front wheel. They have the lowest drag when in use, but also have a slight drag when not in use. But the drag is very low in both cases. The best ones have drag about equal to rising about 5 feet per mile, so it's unlikely that you'd even notice it. They're the best, but the most expensive. They're what most people use now days.

If you want to get into lighting and don't want to spend much to start, you could start with a decent LED light and a bottle generator. Go ahead and spend the money for a decent light, since you will keep it, but go with a bottle generator to get started. Then plan on upgrading to a hub generator down the road. Both bottle and hub generators produce 3 watts at 6 volts AC, so you should be able to use the same light when you upgrade.

Just be careful to get a light that has a on/off switch. Lights are sometimes sold as "for bottle generators" that don't have a switch, because you can turn it off my disengaging the generator. But when you upgrade to a hub generator, your light will always be on. Although, the drag from a hub generator is low enough that some people just keep their lights on all the time to be more visible during the day. Only do this with LED lights, since you'll go through too many light bulbs with halogen lights. For that matter, only get LED lights, they are far superior to the halogens now days.

A good page on generators is http://www.nordicgroup.us/s78/dynamo.html although it is a couple of years old, and at least one link is out of date (the link to the bottom bracket generator at www.bicycletires.com - they no longer seem to carry it). Also, www.peterwhitecycles.com also has lots of good info.

Keith