There are thousands of varieties of vegetables that are practically unseen on supermarket selves. Called "heirloom" vegetables, these varieties have been cultivated by seeds passed down by generations of growers. Some, such as the Brandywine Tomato above, are said to be the most flavorful of their kind. Others varieties include the seeds descended from the vegetables Thomas Jefferson planted at Monticello and the seeds carried by the Cherokee during the Trail of Tears march.
Unlike commercial hybrids, if you grow these vegetables, you will be able to save the seeds yourself, and plant them in the next growing season.
The "Seed Savers Exchange" is the largest organization worldwide devoted to saving heirloom vegetables.
"The Garden Watchdog" has extensive reviews of seed vendors.