The Prius Amberjac is a standard Prius modified with better batteries and plug-in capability (so the increase in mpg comes at a cost of more electricity taken from the power grid). These changes mean the Prius can go 30 miles before the gas engine kicks in and will regularly get 100 mpg. The conversion is expensive, costing thousands of dollars, but the machinery can be moved to another Prius later. Amberjac will soon apply this conversion technology to the Lexus RX 400h, and a lower cost Prius conversion will also be available.
[Source: Independent, Mixed Power]