small heirloom tomatoes
Heirloom tomatoes are non-hybrid tomatoes that are open-pollinated. They're found in a variety of colors, shapes and flavors. They are sweeter, and have a shorter shelf life than regular tomatoes.
Heirloom tomatoes have traits that are less desirable from a commercial standpoint and so it's harder to find them, but in the spirit of genetic diversity there are many farmers who still grow them (ref).