Weed-eaters. The following articles tend to be somewhat specific to their locales, but a lot of the info still applies (and it seems a lot of weeds grow everywhere; nettles and dandelions seem to be as global as death and taxes.)
- Weeds in Your Garden? Bite Back!
- Why Eat Wild Food?
- Edible Weeds (Italy-specific; still looks reasonably useful)
- Live off the land by eating weeds
- CUTTINGS; Eating Weeds For Health (Health benefits of some weeds.)
- Photo gallery of weeds
- Eat your weeds! (short MetaFilter discussion.)
- Local Teens Eating Hallucinogenic, Deadly Weeds (Don't eat Datura.)
(Summary: Dandelions, Lamb's Quarters, Chickweed, Nettles, and something called Purslane are all good and quite popular.)