Hub dynamos. More efficient than bottle or bottom-bracket dynamos, and more expensive. The Shimano is remarkably good value at around £45 (2001 price) - just over a third of the price of the Schmidt - but of course you'll need a wheel built round it. If you live in Reading, that's no problem: just call Bob Bristow.
As with all dynamos, power output is limited to 3W (the LiteSpin reputedly has a higher output which allows a 3W front lamp plus a rear lamp). Even running all of this through a halogen front lamp, light output is only adequate. That's a judgement you make - I ride across country to & from work, so I use a head torch as well in the winter, but I found the light adequate in all but the darkest places. The upside is that it's always there: no flat batteries, no remembering to recharge. With the Shimano you don't even need to remember to switch the lights on, as there's an automatic light-sensitive switch.
Why would you buy a hub dynamo instead of a bottle, then?
Rolling resistance is exceptionally low. OK, you can lift a bottle off when it's not in use, but the resistance of a hub when not powering lights has been calculated to be the equivalent of about one foot climbed per mile. That's less work than the extra weight of a battery lamp (although the Nexus is also fairly heavy). The resistance when powering is definitely lower, and there's none of that rubbing on the sidewall stuff, so it won't slip and go dark in the rain. This also means that little maintenance is required - just the occasional repacking with grease, which is common to most hubs. The automatic switch is a plus, as it is electronically controlled so you can put the lights on on the move without risk of blowing the lamps.
The only significant downside is the weight: around 650g (still less, though, than the battery for a rechargeable lighting system).
The key question is, if I were building another commuting bike, would I buy the same again? Probably - and if I were going with a dynamo again, certainly. I am tempted by the higher light output of rechargeable systems, especially on dark Wednesday evening rides, but ultimately the Shimano hub has been completely reliable with no maintenance through one winter and that is a very persuasive argument. It's there if I happen to leave work late in the summer, as well. Yes, I think it's a must for my commuting bike.
I rate this product 9/10 and would recommend it to anyone who is intending to use dynamo lights. It is about perfect for a commuter bike.