Here's an update for seasonal (North American) summer foods (June-August):
Apricots
Beets
Bell Peppers
Blackberries
Blueberries
Cantaloupe
Cherries
Corn
Cucumbers
Eggplant
Grapefruit
Grapes
Green Beans
Limes
Nectarines
Passion Fruit
Peaches
Peas
Plums
Radishes
Raspberries
Strawberries
Tomatoes
Watermelon
Zucchini
And of course, Eat the Seasons has a list updated week by week based on your location Canada/USA or UK/Ireland.