American Society for Horticultural Science

Bent Creek Institute - Germplasm Repository

Botany Encyclopedia of Plants and Gardening

Civic Garden Center of Greater Cincinnati

epic - electronic plant information centre

Food Timeline (provides an historical look at the introduction of foods - includes lots of herbs, fungi, grains, etc.)

The Garden Gate

Garden Guides

Garden Rant (this is a blog site about all things gardening)

Garden Resources (this is a British site)

Greenroofs.com

The Huntington Botanical Gardens

The International Plant Names Index

KidsGardening!

Kingdom of Fungi (with photo identification of numerous species)

Mazes and Labyrinths, W. H. Matthews (1922) (online book)

Missouri Botanical Garden

National Gardening Association

New York Botanical Garden

Rain Garden How-To

Royal Botanic Gardens, Kew

Royal Horticultural Society

The Treehouse Guide

United Plant Savers

USDA Plants Database

WikiGardens (This site is user edited, so keep that in mind when using it)

Wild Ones, Cincinnati Chapter