Pingyao in Shanxi province is beautiful. It's the best showcase of preserved Ming architecture in the country.

Pingyao is on my toplist too, but I think Wuzheng, etc those small town around jiangsu and shanghai are all good...

Pingyao is great. My advice is to go there and stay in one of the guest houses for a couple of days and enjoy it when it is less busy once all the day tourists leave. While they are there it is just hoards of people buzzing around in those annoying golf carts. Once they have gone you can stroll around or bicycle at your leisure, enjoy the food and soak up the atmosphere with a few cold beers with the other travelers.