World Hardiness Zone Finder
"A hardiness zone is shown on the scale to the right; or usually shown on a map... These zones show a geographically-defined area in which a specific category of plant life is capable of growing, as defined by climatic conditions, including its ability to withstand the minimum temperatures of the zone. The zones were first developed by the United States Department of Agriculture (USDA) and have subsequently been adopted elsewhere."
Source: http://en.wikipedia.org/wiki/Hardiness_zone
Hardiness Zone Maps from Around the World:
Africa: http://www.backyardgardener.com/zone/africa.html
Australia: http://www.anbg.gov.au/hort.research/zones.html
Canada: http://www.planthardiness.gc.ca/
China: http://www.ars.usda.gov/Main/docs.htm?docid=9815&page=2
Europe: Hardiness Zone Map of Europe
Japan: http://www.jelitto.com/english/japan.htm
Russia: http://www.mobot.org/MOBOT/Research/russia/climatic.shtml
South America: http://www.backyardgardener.com/zone/sazone.html
USA: http://www.garden.org/zipzone/index.php?img=seusa