Plug in hybrid electric vehicles (PHEV) have been popping up since garage tinkerers got hold of the Toyota Prius and started experimenting. Instead of relying on the gasoline engine and regenerative braking to do all of the recharging, they asked, quite logically I think, why not plug in to the power grid to recharge when the car is parked?
Toyota and other manufacturers have been reluctant to go along with the PHEV companies, voiding warranties and such, but I think that attitude has been softening to the point where the manufacturers may OK the idea.
At any rate, a Toronto, Ontario company, Hymotion, is coming out with kits for the Prius and Ford Escape which will add a Lithium Ion battery pack and associated electronics so the vehicles can just plug into a wall outlet when parked. Once the batteries are discharged, normal operation returns. The kits aren't cheap and on top of the premium paid for the hybrid car itself, this may not have a huge market with individuals though the company is targeting fleet buyers to begin anyway.
I have never understood why the manufacturers didn't start out building hybrids this way. If you have a big battery and you park the car, isn't a plug just natural?