Ohm’s XS700 was recently reviewed by Wired Magazine, who claimed the electric power system’s nine different assist levels give it the versatility for most situations, including light off-road duty.  Even with an aluminum frame, it weighs in at 53lbs, but the 38V motor gives it the oomph to get you up rolling hills with little or no pedal effort depending on your mood.
It comes with solid componentry, including a full Shimano (mostly Deore) drivetrain, Ritchey cockpit items,  RockShox shock, hydraulic disc brakes and Kenda tires.  MSRP is $3,450, which is quite a bit for a bike, but not entirely out of line among many newer electric bicycles introduced at Interbike last Fall.