This flower, Coreopsis lanceolata, comes up every year and is beautiful. It is very successful at propagating and spreads quickly. I like this in a blooming flower, but not in a weed. It has literally taken over.
I had a bit of a search for the actual name: Lance leaved coreopsis.
About 5 years ago a neighbour gave us a clump of a few flowers. We planted it in our front yard that gets full sun. It has grown and expanded every year, irregardless of a hard or mild winter. While the roses are temperamental and need care, the coreopsis needs nothing.
The coreopsis grows to about 1.5″ tall and will crowd out other plants. In the photo with the purple cransbill geraniums can you see a small pine tree trying to get sun? It is native to Ontario.