Other Industry Associations:
PLANET
Professional Grounds Management Society
Illinois Arborists Association
International Society of Arboriculture
Tree Care Industry Association
Utility Arborist Association
SMA - Soc of Municipal Arborists
American Public Works Association
Garden Centers of America
Your Green Roof Industry Association
APLD - Association of Professional Landscape Designers
  APLD - Midwest Region
ASLA - American Society of Landscape Architects

Plant Searches:
OGA Online Plant Locator
Plant Information Online

Contractor Searches:
ILCA
WISLF

Conservation/ Native Plants:
Midwest Ecological Landscaping Association
Illinois Native Plant Society
IL Native Plant Guide
The Land Conservancy of McHenry County
Openlands
McHenry County Defenders
GreenScreen - Environmental Television for McHenry County
American Forests
Plant Native

Gardens:
The Morton Arboretum
Chicago Botanic Garden
Anderson Japanese Gardens
University of Wisconsin-Madison Arboretum

Research:
TreeLink: The Urban Forestry Portal
American Society For Horticultural Science
UFind the Urban Forestry Index
American Journal of Botany