I have a cheap Shark 500 USB rechargeable light for commuting, and I like it. It was $38 on Amazon, I believe, and came with a USB rechargeable taillight, too.

I don't have experience with Dynamo hubs, though.

I use a wall-USB charger to charge the Shark 500 instead of the inefficient trickle-charge of plugging the microUSB adapter to a USB port on a computer. I still carry a cheap, dim AA powered bike light as backup, because sometimes I get taken by surprise by the Shark 500 losing juice.

While I don't have to worry about theft, as I can store my bike indoors at work in a locked room, I do like the quick on-off of the Shark 500 that others have mentioned.

I ride on MUPs early in the morning (5:30), and the Shark 500 is bright enough for me. Do I sometimes wish I had something brighter? Yes, but only because of other commuters who blind me with their ridiculously bright lights, haha.