With the California Air Resources Board's recent vote to require plug-in hybrids in the state by 2012, a decision likely to be followed by as many as 12 other states, this little corner of the green-car world is about to take off. Here are two companies ready to fly.

Plug-In Conversions of Poway, Cali-fornia, makes the already efficient Toyota Prius into an even more efficient plug-in hybrid, one of which we got to drive. The company has converted five Priuses since last June, with orders for 25 more.

"It's a pretty critical thing," said CEO Kim Adelman. "It just has to be done."

Plug-In Conversions adds an extra nickel-metal-hydride battery pack to the Prius and offers as much as 100 mpg for the first 50 miles of driving (discounting the energy used to generate the electricity, which is typical of these claims). Depending on the pack size, it can go 24 miles on battery power alone, too ...