Well, the electricity just keeps flowing in bikes.  Infineum of the UK has released an electric-assisted mountain bike, complete with Rock Shox fork and Cane Creek headset.  Two features make this unique (well, three, if you consider that you can actually ride this off-road) among electric bikes.
First, the battery packs are stackable, with each one good for 25-30 miles of full electric coasting.  Add more as your journey / physical ability dictates.  Second, the power assist level is adjustable, meaning you can have it help you a little, or coast along without pedaling at all, up to 15mph.  Check their website for detailed specs.
