You should take a look at the product of this austrian company if you're looking for good-looking E-Bikes that don't look like E-Bikes at all.
They put their motor in the seat tube and it merely assists the pedaling,
Aside from the battery pack that disguises as a tool-pack right underneath the saddle you can't see it's an electric bicycle on the outside.
Their system is supposed to work in almost any off-the-shelf frame (with limitations for carbon frames).
They also have some carbon frames that work with their system, though apparently this doesn't work with most "stock" carbon-frames.
Have a look at their website: http://www.vivax-assist.com/en...