U of Illinois at Urbana Champaign Weed Science has a web site with both edible and non-edible weeds mixed. No edibility info. See Weed Identification with six categories in a frame along the left that narrow the hits displayed on the right. The Weed Science Society has a weed image archive . Also see the index Intriguing World of Weeds .
Site can be slow.
Also there is a Weed Science site which is a ways from completion. The Cornell Poisonous Plants Page is helpful for knowing what not to forage for. Mark's Fruit Crops is a site by a Professor of Horticulture where you'll find information on the taxonomy, history, production, medicinal and nutritional properties, general culture, and post harvest handling of over 30 of the world's major fruit crops. The list that is the most foraging oriented is wild- edibles . Active but most posts are on topic.