Another option is a bottom bracket mount dynamo. Supposed to be quieter andmore efficient than the bottle dynamos though not as low drag as the hub dynamo. Peter White Cycles is bringing in the Sanyo model and selling it for less than the Dymotec 6 bottle generator, $44.
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Gear Hubs Owned: Rohloff disc brake, SRAM iM9 disc brake, SRAM P5 freewheel, Sachs Torpedo 3 speed freewheel, NuVinci CVT, Shimano Alfine SG S-501, Sturmey Archer S5-2 Alloy. Other: 83 Colnago Super Record, Univega Via De Oro
Visit and join the Yahoo Geared Hub Bikes group for support and links.
http://groups.yahoo.com/group/Geared_hub_bikes/