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Leafy greens (spinach, kale, chard, etc), broccoli, brussels sprouts, cauliflower, yams, squash, red/yellow/orange peppers, cucumbers, etc etc...
This is from "Ask Mary" of Calorie Count fame:
"Vegetables that contain more water are usually lower in carbohydrate and calories. Low sugar vegetables include tender green leafy vegetables (spinach, lettuce, salad greens), asparagus, cucumber, radish, cabbage, celery, broccoli, cauliflower, and mushrooms. Root vegetables and those with less water are highest in sugar. Examples are green peas, corn, winter squash, beets, white potatoes, and sweet potato. Every other vegetable is somewhere in between."