Community organizations, businesses, and other establishments that support the urban food movement:

US Organizations
Food Hub - One-stop shop for regional foods.
The Greenhorns - To promote, recruit, and support young farmers

Boston, Massachusetts:
Green City Growers - Farm fresh food right from your yard
The Food Project - Engaging young people through sustainable agriculture

Detroit, Michigan:
Garden Resource Program - Providing residents with resources to grow food in the city. 
RecoveryPark - Planned community redevelopment project for the city of Detroit that will include urban farming among other sustainable initiatives

New York City, New York:
EcoStation: Bushwick - Greening NYC one block at a time
Just Food - Increasing access to fresh, healthy food in NYC
Western Queens Compost Initiative - Leadership, service, and education in composting

San Francisco, California:
The Center for Urban Education about Sustainable Agriculture
Cultivate SF - Catalyzing the development of self-sustaining urban agriculture ventures
Free Farm Stand - Making local grown food accessible to all
Garden for the Environment - Acclaimed one-acre urban demonstration garden
Kitchen Garden SF - Raising awareness of and accessibility to kitchen gardens
Oakland Based Urban Gardens - Building healthy communities
Oakland Food Connection - not-for-profit focused on Oakland's heritage of food, community and culture
People's Grocery - Healthy food for everyone
San Francisco Environment - helping all SF residents take an active role in protecting and enhancing their urban environment.
San Francisco Urban Agriculture Alliance - Greater access to and consumption of SF grown food through advocacy, education, and grassroots action.
San Francisco Permaculture Guild - Bringing people together towards permaculture for a village renaissance in the urban pulse of the city of San Francisco.
Sunnyside Organic Seedlings - Supplying organic seedlings to the Bay area.
The Urban Farmer Store - San Francisco, Mill Valley, Richmond

Vancouver, Canada:
Eat Drink Be Local - Insider's guide to good things local.

(Data is continually being added to this page. Please contact growingCities with tips about other relevant establishments.)