What crops are grown in market gardening?

When you garden for the market you want to have something that will grow well in our USDA Zone, something that is appropriate for the season and something the customers will enjoy. In the summer there are the staples of beans, tomatoes and squash. In the winter the greens abound as well as turnips, beets and onions. Some people try to grow veggies that really aren't meant for their area, but this should only be done for fun and not for profit.