A great reseeder is several of the nemesias, specifically these two:
I started out with only a couple in pots and I now have them all over the garden, coming up in different variations too.
Bill Wallis geranium is also a great reseeder, started out with one years ago from Anne's Annuals and it's every where. I pull them where I don't want them. They intermingle with the shrubs, roses and daylilies so nicely. A couple of older shots.
