Additions for the coastal PNW area:
Our snowberry is not edible by humans from what I understand! Please leave it for birds!! (edit: the common snowberry in the west is not edible, but as the helpful commentor below says there are multiple plants called snowberry in different families!)
Oregon grape berries are sour and best mixed with other berries if not used in preserves. Goes well with that late season salal.
Manzanita berries (as well as bearberry, there are multiple other species of manzanita) are edible but I would leave them for the bears, they are dry and not tasty. (edit: maybe some types are good to eat? or other people here have a broader palate than I...)
The following are plants that I have personally tried:
Beach
Pea, Lathyrus japonicus - an good tasting pea that grows in decent sized patches on and near beaches. Everlasting pea is also edible but not quite as tasty, it fruits later in the year. Make sure not to eat large quantities regularly, relying on wild peas or vetch for a large portion of your diet will kill you slowly. (probably how Chris McCandless died)
Broadleaf Dock, Rumex obtusifolius - naturalized old world weed. Grows just about anywhere but tastiest in the shade and in good soil. I ate a lot of this plant from logging roads in northern CA. Throw it in ramen, beans, or anything else that could use a sour potherb. I wouldn't eat it raw.
Candyflower (Siberian Miner's Lettuce, as well as Miner's Lettuce. not much difference) - excellent snacking herb, I've only eaten it raw. Grows in the forest of southern OR and northern CA wherever it can find a little sun. One of the best and most common wild greens in my opinion.
Hedge
Bindweed - per a suggestion in another post on this site, I fried up a big handful of the hedge bindweed taking over various corners of my
yard. Very nice cooking green, not bitter, far better than false dandelion. Make sure you identify it correctly, by flowers should be the easiest way but it does closely resemble other bindweeds that may not be edible.
Purple Dead Nettle (aka red dead nettle) - if you don't mind a fuzzy texture, this is a great snacking herb during the spring! I just eat the tops wherever I see them. Naturalized old world species, grows in meadows and lawns.
Salal - this is probably the most important berry in my region, the only other plant that even comes close is huckleberry. Grows from the Northern California coast to I'm not sure how far north, but extremely common in coastal Oregon. Berries are delicious reaching their full flavor when they begin to look overripe or even dehydrated on the plant.
Sedge - all sedge seeds are edible to my knowledge. I've begun experimenting with slough sedge, my first attempt cooking left it tough to chew but the flavor was very good! Hopefully it is possible to soften to the point where it is easy to eat a bowl, but either way this is a great food in my opinion. Slough sedge is fairly common in southern OR coast, it should be possible to gather decent amounts if you can find a non-polluted area where it grows.
Three Cornered Leek, Allium triquetrum - an naturalized / invasive old world onion. This is the species of choice for wild onion in coastal OR. At the right time of spring you can see these everywhere around yards and unmanaged spaces near towns. You can eat the whole plant, I prefer the immature flower buds for texture and ease of collection. You can also find their bulbs in the ground but unless you know exactly where a patch is I wouldn't recommend trying to identify in their dormant season. Remember that if it doesn't smell like onion, it's not Allium and possibly poisonous.
Tree Mallow - the variegated type is naturalized in southern OR and northern CA, mostly around people's yards. Edible seeds without a strong flavor, mostly good for a few mouthfuls as a snack unless you happen to have a lot of big ones near you.
Tule (Bulrush) - very common, wonderful rhizomes, easy to gather, the youngest rhizome can be eaten fresh and older rhizome pounded and dried for flour. Unfortunately I haven't been able to experiment very much with this plant, because it is a wetland plant that will soak up any pollution in the area. I would eat it from my patch near the highway if I absolutely had to, or after the blessed day that the road closes forever.
Another edit: I haven't personally tried it, but the edible part of Yellow Pond Lily is said to be the seeds after allowing the fruit to rot in water for several weeks. They are said to be quite good popped, I meant to get some but I think I missed the season this year...