My friend Jim suggested this post, and I'm glad he did. He's apprehensive about joining a CSA; he seems especially concerned that he'll end up with 200 boxes of radishes. Here's a month-by-month listing (from the Harmony Valley Farm website) that lists the vegetables (and occasional fruits) that will be coming from the Harmony Valley Farm CSA, located in Wisconsin.
Although this list reflects only one particular farm, I'm going to go ahead and guess that the foods are (at least) similar to those you'd get from other Wisconsin and Minnesota CSAs. I hope you find it useful.
May Arugula, Asparagus, Garlic (green garlic, scapes), Horseradish, Onions (red, yellow, cipollini, shallots), Ramps (wild leeks from the woods), Rhubarb, Salad mix, Spinach, Sunchokes
June Arugula, Basil, Beets, Broccoli (and broccoli romanesco), Currants, Fennel, Garlic (green garlic, scapes), Greens (chard, kale, bok choi, etc.), Herbs (cilantro, dill, chives, sage), Kohlrabi, Leaf lettuce (escarole, endive), Onions (red, yellow, cipollini, shallots), Peas (snap and snow), Salad mix, Sauté greens, Spinach, Strawberries, Turnips (purple top, gold, scarlet, white), Zucchini (and summer squash)
July Arugula, Basil, Beets Broccoli (and broccoli romanesco), Carrots (orange, red and yellow), Cauliflower (white, purple, green), Cucumbers, Garlic (green garlic, scapes), Green beans (French, haricot vert), Greens (chard, kale, bok choi, etc.), Herbs (cilantro, dill, chives, sage), Onions (red, yellow, cipollini, shallots), Peppers (sweet bells/hot), Potatoes, Salad mix, Sweet corn, Zucchini (and summer squash)
August Arugula, Basil, Beets Broccoli (and broccoli romanesco), Cantaloupe/watermelon, Carrots (orange, red and yellow), Cauliflower (white, purple, green), Cucumbers, Edamame (fresh soybean), Eggplant, Garlic (green garlic, scapes), Green beans (French, haricot vert), Greens (chard, kale, bok choi, etc.), Herbs (cilantro, dill, chives, sage), Onions (red, yellow, cipollini, shallots), Peppers (sweet bells/hot), Potatoes, Sweet corn, Tomatoes (hybrid, heirloom, cherry), Zucchini (and summer squash)
September Arugula, Basil, Beets, Broccoli (and broccoli romanesco), Cabbage (red, green, savoy, napa), Cantaloupe/watermelon, Carrots (orange, red and yellow), Cauliflower (white, purple, green), Celeriac, Cucumbers, Edamame (fresh soybean), Eggplant, Fennel, Garlic (green garlic, scapes), Green beans (French, haricot vert), Greens (chard, kale, bok choi, etc.), Herbs (cilantro, dill, chives, sage), Onions (red, yellow, cipollini, shallots), Peppers (sweet bells/hot), Potatoes, Raspberries, Salad mix, Sauté greens, Spinach, Tomatoes (hybrid, heirloom, cherry), Winter squash (butternut, festival, etc)., Zucchini (and summer squash)
October Beets, Broccoli (and broccoli romanesco), Brussels sprouts, Cabbage (red, green, savoy, napa), Cantaloupe/watermelon, Carrots (orange, red and yellow), Cauliflower (white, purple, green), Celeriac, Daikon and beauty heart radish, Garlic (green garlic, scapes), Greens (chard, kale, bok choi, etc.), Kohlrabi, Leaf lettuce (escarole, endive), Leeks, Onions (red, yellow, cipollini, shallots), Parsnips, Potatoes, Raspberries, Rutabaga, Salad mix, Sauté greens, Spinach, Sweet potatoes, Turnips (purple top, gold, scarlet, white), Winter squash (butternut, festival, etc.)
November Beets, Brussels sprouts, Cabbage (red, green, savoy, napa), Carrots (orange, red, and yellow), Celeriac, Daikon and beauty heart radish, Garlic (green garlic, scapes), Horseradish, Kohlrabi, Leeks, Onions (red, yellow, cipollini, shallots), Parsnips, Potatoes, Rutabaga, Sunchokes, Sweet potatoes, Turnips (purple top, gold, scarlet, white), Winter squash (butternut, festival, etc.)
December Beets, Brussels sprouts, Cabbage (red, green, savoy, napa), Carrots (orange, red, and yellow), Celeriac, Daikon and beauty heart radish, Garlic (green garlic, scapes), Horseradish, Onions (red, yellow, cipollini, shallots), Parsnips, Potatoes, Rutabaga, Sweet potatoes, Turnips (purple top, gold, scarlet, white), Winter squash (butternut, festival, etc.) 
January Beets, Cabbage (red, green, savoy, napa), Carrots (orange, red and yellow), Celeriac, Daikon and beauty heart radish, Garlic (green garlic, scapes), Horseradish, Onions (red, yellow, cipollini, shallots), Parsnips, Potatoes, Rutabaga, Sunchokes, Sweet potatoes, Turnips (purple top, gold, scarlet, white)
For an additional cost, Harmony Valley also offers a fruit box, featuring fruits from all over North America (not just the Midwest). As you can see, although there are no bananas, the list is pretty wide-ranging.
June – October Apricots, Avocados, Blueberries, Bing & Ranier Cherries, Fresh Figs, Grapes, Mangoes, Nectarines, Peaches, Pineapple, Pluots, Plums
November – January Pink Lady Apples, Blood Oranges, Cranberries, Medjool Dates, Rio Star Grapefruit, Asian Pears, Bosc Pears, Mandarines, Mineolas, Cara Cara Red Navels, Meyer Lemons, Pomegranates, Tangerines, Clementines, Mangoes
