No offense to Trulia, if they offer this, but sites that show current values like Zillow and others are just not very accurate.
I can email you information like this that's going to get you the most accurate numbers possible that I know you're looking for. I am limited to doing this by city for something I can email to you. As opposed to by county. If you can let me know what city or even more specifically a particular area that I can pinpoint & map, I can break it down and email you 2008-2009 monthly stats for solds. At the bottom of each list it will automatically tally up the avg. price per square foot.
As I said, if you can be city, area, or neighborhood specific, I can email you these figures in under 20min.