My plan is to soon dig up most of the maroon poppies that have seeded themselves thickly every year for the last decade or so. While the flowers are divine, and the bees get absolutely blissed out in them, they take up so much space, and are not attractive unless actually flowering. I know they will always come back, so it's not as if I'm losing future options.
Nigella or love in the mist have seeded like a thick carpet. I love its ferny leaves and how it blends with its siblings and other plants, even when not flowering. Removing the poppies will enable individual plants to spread out a bit. At times I have planted other colours than the usual blue, like mulberry and white, but the blue ones are the strongest, and they are the ones that mostly re-seed.
The other wildflowers I treasure are California poppies - they seem to be virtually indestructible. My favourite varieties are the cream flowers with frilled petals.
In past years I had an absolute carpet of blue forget me nots, I still have them, but not in dramatic carpet dimensions.