The first fruit you think of when you hear the word "heirloom" is probably the tomato. You can find heirloom varieties on summer menus all around the country, and might even be growing some yourself. But think a little bigger--heirloom watermelons are starting to catch on.
I've seen this most in Georgia, a big watermelon state, where some farmers and restaurants are moving towards using the more flavorful (but not commercially viable) heirloom melons. The melon you'd find down at the supermarket has been bred over decades to have a thicker rind so that it can make the trip across the country without busting open in the truck, but that durability comes at the price of flavor.
Flavor aside, though, one of the best parts of heirloom anything is that you get to use their crazy names--instead of just saying you're eating a watermelon, you get to say you're eating a Georgia Rattlesnake, a Sugarbaby, or a Moon and Stars. Even just visually, it's nice to see something besides the same old bright green rind and red flesh. The Moon and Stars, for instance, is a dark, deep green, with just a few flecks of yellow (get it?), and varieties like the Orange Crisp and Yellow Doll are actually orange and yellow on the inside.