This plant is abundant and about 6 feet tall. It's blooming with pretty blue berries this spring.

Going out on a limb, maybe some sort of wild lowbush blueberry (Vaccinium angustifolium)? Don't take my word for it, just a wild guess.

I thought that, because blueberries are so common here, but the berries don't look quite like blueberries? Maybe as it grows I'll be able to tell.