Although used car prices likely peaked in June, average trade-in values of many popular, fuel-efficient small cars for the 2006-2009 model years are still expected to be 10 to 30 percent higher in August 2011 than they were at the beginning of the year, says Jonathan Banks, senior analyst with the NADA Used Car Guide.

For example, average trade-in values for the Toyota Prius are expected to be 30 percent higher in August 2011 compared to January 2011, according to the NADA Used Car Guide. Over the same time period, the Chevrolet Aveo is expected to be up 21%, Kia Spectra (up 19%), Hyundai Accent (up 17%), Nissan Versa (up 16%), Ford Focus (up 15%), Honda Civic (up 14%) and Dodge Caliber (up 13%).

"Car owners still have a lot of equity built up in their used cars, which puts them in a better financial position to make a down payment on a new vehicle," Banks said. "Looking ahead to the fall, we expect prices on used small cars to drop slightly as consumer demand for new cars increases with the arrival of the 2012 model year, a new round of manufacturer incentives and moderating gasoline prices."