The best output for your pedaling effort, and for your money, seems to be the Forumslader V5. It comes as a kit, which I think is within my capabilities to assemble. I haven't figured out how to actually order one, though; their website says "order by email", but gives no address. Does anyone have one?

One downside to the Forumslader is that it requires you to switch off the bike lights to charge a device. Of course, when the lights are on, there is much less power available for any charger to harvest, but I found (somewhat to my surprise) that the B+M USB-Werk would work fine with the lights in "daytime running light" mode. If all I'm doing is keeping my GPS topped up, there is plenty of power. Many other chargers have the same "feature", I've been learning.