The Ivillage Great garden site. Experts answer your plant questions when you email them. http://gardenweb.com
Here you can contact your local Cooperative Extension service http://npic.orst.edu/pest/countyext.htm you can send soil samples, get bug problem solutions. Just click on your state for further information.
Better Homes and Garden, especially their container gardening information. There is also plant zone information. http://www.bhg.com/gardening/
http://www.hgtv.com/topics/container-gardening/index.html I usually go to this site for their great container gardening ideas.
So much information here and the photos are gorgeous. http://awaytogarden.com/