I picked this up a few months ago from another 3FC IPeep's post. Don't have the name to give the credit to, but whoever you are, thank you!
Another helpful link from the idealcoachingtv site is
http://nutritiondata.self.com/ Click on "Foods by Nutrient" then there are several ways you can search. I came up with the following reference for myself (most are 'raw' measurements). Having a digital food scale to weigh by grams would be very helpful for things not easily measured in a "cup":
Asparagus (1c, 134g) 5 carb - 3 fiber = 2 net carbs (3g sugars)
Broccoli (1c, 91g) 6 carb - 2 fiber = 4 net carbs (2g sugars)
Brussel Sprouts (1c, 88g) 8 carb - 3 fiber = 5 net carbs (2g sugars)
Cauliflower (1c, 130g) 6 carb - 2 fiber = 4 net carbs (2g sugars)
Cabbage, green (1c, 89g) 5 carb - 2 fiber = 3 net carbs (3g sugars)
Celery (1c, 100g) 3 carb - 2 fiber = 1 net carb (2g sugars)
Cucumber w/peel (1c, 133g) 3 carb - 1 fiber = 2 net carbs (1g sugars)
Green beans, cooked (1c, 125g) 10 carb - 4 fiber = 6 net carbs (2g sugars)
Kale, fresh (100g) 10 carb - 2 fiber = 8 net carbs (0 sugars)
Mushroom, portabella (100 g) 5 carb - 2 fiber = 3 net carbs (2g sugars)
Mushroom, white (1c, 70g) 2 carb - 1 fiber = 1 net carb (1g sugars)
Onion, raw (1c, 160g) 15 carb - 3 fiber = 12 net carbs (7g sugars)
Red bell pepper (1c, 149g) 9 carb - 3 fiber = 6 net carbs (6g sugars)
Rhubarb (1c, 122g) 6 carb - 2 fiber = 4 net carbs (1g sugars)
Rutabagas (1c, 140g) 11 carb - 4 fiber = 7 net carbs (8g sugars)
Sauerkraut (1c, 142g) 7 carb - 4 fiber = 3 net carbs (3g sugars)
Snowpeas (1c chopped, 100g) 7 carb - 3 fiber = 4 net carbs (4g sugars)
Summer Squash (yellow/zucchini) (1c, 110g) 4 carb - 1 fiber = 3 net carbs (2g sugars)
Turnips (1c, 140g) 8 carb - 2 fiber = 6 net carbs (5g sugars)
V8 juice (note 1/2c, 120g) 5 carb - 1 fiber = 4 net carbs (4g sugars)