If you like surprises, consider planting Columbine (Aquilegia).
A Columbine plant lives only a few years, but will generously self-seed. Not only do you never know where one might take root, you never know what shape or color might appear, as the seeds do not grow true to the parent. Seedlings are easily pulled or transplanted, but the fact that they could pop up anywhere is part of their charm, and I often leave them where they land. Should you want to remove the seedpods and plant the seeds more deliberately, simply sprinkle them on the ground. There’s no need to cover the seeds with dirt.
Columbines will grow in sun or shade, but prefer shade in very hot locations. Their foliage is attractive, and their flowers sway in the slightest breeze, earning them the nickname ‘Dancing Ladies’ here in our neighborhood. They begin to flower in May, and deadheading will encourage additional blooming throughout the summer.