You've heard this term by now, haven't you?

CSA, Community Supported Agriculture, is partnership between the community and the farmers or growers whereby CSA Members support the farm throughout the season, assuming either all or part of the costs and risks, and in return the farmers commit to offering a wealth of seasonal, fresh produce to the Members. The system creates a link between people and the food they eat, the land on which it is grown and those who grow it.

Many farms offer produce subscriptions, where buyers receive a weekly or monthly basket of produce, flowers, fruits, eggs, milk, coffee, or any sort of different farm products.
A CSA, (for Community Supported Agriculture) is a way for the food buying public to create a relationship with a farm and to receive a weekly basket of produce. By making a financial commitment to a farm, people become "members" (or "shareholders," or "subscribers") of the CSA.

Many communities have websites or other information on local CSA's.

Some additional sources:
Local Harvest
The usda's information on alternative farming
Green People's list
Food Connect (in Australia)