I haven't read all the responses, but I've a;ways had good luck with cleome. So good, I hust throw the seeds where I want them to grow, andwhen they're done flowering and go to seed, I harvest seed for the next year. The ones that fall there, sprout and bloom, in fact you can even take the seed and sow it late in the fall.
Another one you can just 'throw' the seed is nigella