After years of study and speculation, Toyota today unveiled two new Prius vehicles at the 2011 Detroit auto show. By the time all the curtains were opened, four Prius models were displayed on stage: the familiar 50-mpg hatchback model; the Prius plug-in demo version with the same shape; a new larger model that goes on sale this year; and a small city concept Prius that promises to offer the best price and highest mpg of any hybrid on the market.