The 2012 USDA Plant Hardiness Zone Map is the standard by which gardeners and growers can determine which plants are most likely to thrive at a location. The map is based on the average annual minimum winter temperature, divided into 10-degree F zones.
Their Interactive Map allows you to "zoom" in on any area of the United States by Zip Code. Below is an example of a Zone Map for the 92590 Zip Code (Temecula, California). Once you enter your Zip Code, you can zoom in and out. It doesn't get much better than that (click on the image below for the high resolution version).