Bluebird Nursery in Nebraska
This is where I buy many of my perennials. If they can grow in Nebraska during the summer - they will grow here.
USDA Plant Database
Great place to lookup information about all plants in the United States.
Tremendous amount of information here.
Iowa State University Extension
Another great place to start looking for information.

Good location with lots more links for basic info and landscaping and more.

Sitting peacefully doing nothing Spring comes and the grass grows all by itself. - Anonymous