The US National Arbor Day Foundation has published an updated "hardiness zones" map, taking into account changes due to climate change. On their web site they've compared the old map (1990) and the new one (2004). Although the map doesn't include Canada, it's quite interesting to see this visual representation of how the North American climate has already changed!
According to their press release "once the Foundation analyzed the new data, hardiness zones were revised, generally reflecting warmer recent temperatures in many parts of the country".
Apparently, the USDA is also working on a new map. However they say that the new map will reflect "weather" changes rather than "climate" changes. Sounds like semantics to me. There is a very interesting article about the planned new USDA map at azcentral.com