I'm not a huge car person, so there are probably people who can be of more help, but...
This would be a place to start:
http://www.consumerreports.org/cro/home.htm
You could also try the auto magazine route - "Road and Track," "Car and Driver," magazines like that.
The Kelley Blue Book is another resource, and now they're online:
http://www.kbb.com/