In 2014 I ran across two plants that are considered weeds or invasives by farmers or botanists, but are good for eating.
The definition of a weed, "a plant growing in the wrong place at the wrong time", applies here.

Miner's Lettuce

The common name miner's lettuce refers to its use by California Gold Rush miners who ate it to get their vitamin C to prevent scurvy.

It is considered a weed at UC Davis' Integrated Pest Management Program

However it is prized as as a gourmet green for salads, especially in Europe.

The great Scots naturalist Archibald Menzies discovered miner's lettuce on the West Coast of America in 1794, and he brought seeds back to England's Kew Gardens, where it flourished.

Miner's lettuce is pleasingly crunchy, mild-tasting, has large leaves, remains tender even when in flower.
100 grams of miner's lettuce -- about the size of a decent salad -- contains a third of your daily requirement of Vitamin C, 22 percent of the Vitamin A, and 10 percent of the iron.

At Foraging for Miner's Lettuce, a World-Class Salad Green | Hunter Angler Gardener Cook, Hank Shaw says,
"Normally I mix greens to create certain flavors and textures (I wrote about making a proper salad a while back), but sometimes I prefer to eat miner's lettuce solo. You really get to know a green when you do this, and you don't want to dress such a salad too heavily; just a light coating is all.

I made a light mustard vinaigrette for the dressing, and added some fresh ground black pepper and a little flake salt for texture and crunch. The effect is tart, smooth, a little crunchy, and very 'green' tasting."

The Territorial Seed Company sells the seeds.

Wine Berries

Wineberries (Rubus phoenicolasius)are thick in Washington Valley Park and undeveloped open space across the street from my house in Martinsville, NJ.

Wineberries are considered an invasive in many states including Pennsylvania.
They ripen in New Jersey at the end of July

Botanically Wineberries, along with raspberries and blackberries, are not a berry but an "aggregate of drupelets", each of which contains a seed, clustered around the receptacle, the cone-shaped core. In wineberries and raspberries the receptacle is left behind when you pick the ripe fruit; In blackberries, the receptacle comes off with the fruit.

Wineberries taste much like flavorful raspberries, but juicer and a bit more sour, and contain similar health benefits - good source of vitamin C, antioxidants, minerals, and fiber. The berries are fragile and, once picked, last only a few days in the refrigerator, but they freeze well. They can be eaten fresh, or used in desserts, fruit salads, and sauces. They make wonderful jam and good wine, too. So, if life hands you wineberries, make wineberry pie!
See also Wineberry (Rubus phoenicolasius) (nps.gov/plants)

Links:
Newsletter 1 April 2014 | Eat The Weeds and other things, too