Every so often I have to slap myself in the head. I'm surprised that we haven't covered these things by now. DeWalt's been selling a LiIon 36 volt battery pack that's full of the latest A123 cells. These are the same ones that were used in the Killacycle. (I think they've got a new batch of cells now).
A while back, [Jeff] sent in a circuit for using multiple packs, leaving the internal BMS in place. [The link is fixed now]
[Robert] sent in a scooter that's been designed to run these same cells. The custom fabrication and machine work looks fantastic.
http://www.hackaday.com/2007/09/05/a123-liion-battery-pseudo-extra/