Because of the many threads that come up on the Brompton yahoo discussion forum about adding electric assistance and that many of the enthiasts like myself have had to type and re-type replies, I have agreed to update the associated area on the Brompton wiki.
As I am not a reseller hopefully it will be independent, although I must confess that having converted several Bromptons to electric assistance I have my favorite components.
However all my conversion have been DIY from motors sourced directly form China i.e. building wheels and adding electrics rather than purchasing the many kits that are now available.
Its still a work in progress, but I have added a few links at the bottom of the page to kit and component providers.
There is also a nice video showing exactly how a kit can be fitted. Although it is provided by a specific supplier the process is pretty similar for the various kits available.
In addition much of the information is also transferable to other small wheeled bikes and folders. I myself have also added assistance to a Dahon Uno and a Xootr Swift.