You might find this site interesting:
food index
My ratings:
Potatoes - 5
Corn - 5
Mushrooms - 7 (suprisingly high in selenium)
Black Beans - 8
Romaine Lettuce - 9
Tomatoes - 10
Artichokes - 7
Squash - 6 (you mean like yellow squash and zucchini? I would rate "winter" squashes higher - butternut squash, acorn squash etc)
Spinach - 10
Broccoli - 10
Cauliflower - 6 (I should eat more cruciferous vegetables, I just loathe cauliflower)
You didn't list:
Red, yellow, orange peppers - 9
Carrots - 9
Sweet potato - 10
Avocado - 8