Also see Growing horseradish, 2.20.1, above.
From: ecoli.cix.compulink.co.uk (Peter Harris)
Marigold and nasturtium. Just sprinkle a few packets around and your only future problem is thinning them down each year.
Then there are the mints (Mentha sp.), horseradish, Artemisia ludoviciana, bouncing bet (Saponaria sp.) and comfrey. They should be planted in containers which are dug into the ground to avoid them taking over the garden, and to make it possible to get rid of them if you decide to. Among the wild seeders are motherwort (Leonurus cardiaca), catmints (eg. Nepeta cataria, Nepeta grandiflora), wild oregano (Origanum vulgare), valerian (Valeriana officinalis), mallows (eg. Malva moschata, Malva rosea), and hyssop.
A prolific annual is California poppy, Eschscholtzia californica.