This Google Map displays the current USDA plant zone hardiness zones. Hardiness zones are helpful in deciding which trees and plants will survive in a particular area.
There are detailed interactive zone maps for each US state, for example this map of California.
It is possible to search zones by zipcode and view zones down to the sub zone level. By entering your zipcode you can also get first/last freeze, heat zones, drought conditions and annual climatology for your area.
You can also embed the zip to zone search in your website using the PlantMaps widget at Hardiness Zone Zipcode Search Widget