Useful Sites & Sources

Gardening Blogs:

Chelsea Green Publishing
Garden Nerd
Girl in an Apron
Homegrown
I Dig My Garden
Leslie Land
Paradise Lot
SeedFreedom

Seeds, seeds, and more seeds:

Aravaipa Heirlooms
Baker Creek Heirloom Seeds

Botanical Interests
Comstock, Ferre & Co.
Dixondale Farms (Family grown onion plants for 106 years!)
Filagree Garlic Farm
Garden Medicinals and Culinaries
Good Seed Company
High Mowing Organic Seeds
Hood River Garlic

Hudson Valley Seed Library
McClure & Zimmerman
Michigan Heirlooms

Native Seeds/SEARCH
Peaceful Valley Farm & Garden Supply
Prairie Moon Nursery: Native Gardener's Companion
Renee's Garden Seeds
Richters Herbs
Select Seeds
Southern Exposure Seed Exchange
Strictly Medicinal Seeds

Sustainable Seed Company
Terrior Seeds | Underwood Gardens
Territorial Seed Company

Victory Seeds
Wood Prairie Family Farm

Fruits:
DeGrandchamp Farms
Nourse Farms
Raintree Nursery

Seed Freedom:
Declaration on Seed Freedom
Monsanto-free seed companies - list originally provided by Occupy Monsanto, but discovered on 07-Feb-2014 that their web domain has expired (OccupyMonsanto360.org). 
Occupy Monsanto 
Safe Seed Resource List - provided by Council for Responsible Genetics (CRG)
Safe Seed Company List - provided by Farm Wars

Flowers and other ornamental greenery:
Annie's Annuals & Perennials
High Country Gardens
John Scheepers, Inc.
Lady Bird Johnson Wildflower Center
Moss Acres
Old House Gardens Heirloom Bulbs

Schreiner's Iris Gardens

Simply Succulents

White Flower Farm

Gardening Tools and Supplies:
Drip Works
Fresh Start
Gothic Arch Greenhouses

Red Pig Garden Tools
Santa Barbara Greenhouses
Texas Metal Sisterns
Uncle Jim's Worm Farm
A list of tool-lending libraries around the world

Weeds, the Soil, and Weed Identification
The Language of Weeds by way of the Chicago Botanic Gardens web site.
Weed Identification by way of the Weed Science Society of America (WSSA) web site.
WEEDS: Don't Shoot the Messenger by Av Singh
Weeds: Guardians of the Soil by Joseph A. Cocannouer

Look to the Weeds by way of homestead.org
Soil Science Society of America

Soil cultivation and Tillage in Organic Agriculture by way of the Food and Agriculture Organization of the United Nations

Miscellaneous Smartness:
American Community Gardening Association (ACGA) - Community Gardens by State, 
Discover Life - caterpillar, moth, bee, ant, and snake identification (to name a few possibilities!)
UCCE - Starting a Community Garden
ACGA - Tools and Sample Forms for community garden start-up
BottlesUp
Build It Solar
Butterflies and Moths of North America
Find Good Food at Homegrown - A resource to find local farms, farmers markets, co-ops, meat processors, CSAs, and more.
Institute for Responsible Technology
Local Harvest - Find local farmers markets, CSAs, farms, events, and more.
National Weather Service - Freeze/Frost Maps
Non-GMO Project
Spiders.us - An international spider community with a North American focus.
ThePrayingMantis.org
The Urban Farmer, Curtis Stone
The Urban Farming Guys

Seed Libraries:
Richmond Grown Seed Lending Library
The Seed Library Social Network

Publications:
Acres U. S. A.
Fine Garden-=ing
Heirloom Gardener
Modern Farmer
Seed to Seed: Seed Saving and Growing Techniques for Vegetable Gardeners by Suzanne Ashworth
The Cut Flower Quarterly
The Heirloom Life Gardener by Jere and Emilee Gettle

Books:
The Backyard Homestead by Carleen Madigan
The Plant Lover's Guide to Dahlias by Andy Vernon
The Backyard Homestead Guide to Raising Farm Animals by Gail Damerow (and others)
Paradise Lot: Two Plant Geeks, One-Tenth of an Acre, and the Making of an Edible Garden Oasis in the City by Eric Toensmeier with contribution by Jonathan Bates
Eric Toensmeier's website
The Urban Farmer by Curtis Stone
The Vegetable Gardener's Guide to Permaculture by Christopher Shein
Epic Tomatoes by Craig LeHoullier