I let my parsley self-sow with great results. I planted both flat-leaved and moss curled, about five years ago, but what seems to have the most success is the flat-leaved. It's great because I don't have to fiddle with seedlings or saving those seeds any more. I haven't planted a parsley in years now, and still I always end up with plenty enough plants for both me and all the black swallowtail butterflies that show up.

I also have let red Russian kale self-seed. Then I try to move the seedlings where I want them.

Mache, chard, red Russian kale and nasturtiums self-sow amongst my vegetables.

I can not eradicate cilantro from my garden. It's a good thing we have developed a taste for coriander, what with all the root vegetables we eat in winter. It comes up and blooms even in full shade. Many good suggestions here, let me add arugula and a japanese red mustard whose name escapes me (and it escapes me because I had the packet long ago, but I still have it in 3 or 4 beds). Parsnip should be in the discussion too.

Borage is also self seeding, and can take over a garden if you don't watch out. I've also had basil grow on its own when I discard the pinched off flowers in the garden.

I'm jealous of glib. I can't grow cilantro for more than a week, and I love salsa.

Here is a link that might be useful: What's Growing On?

Japanese shiso herb self-seeds rampantly. In the U.S. it is called perilla. They are shallow-rooted annuals and easy to pull, but their sheer numbers may overwhelm a person.

It comes in red and green.

My borage self-seeds as well. Cute, cucumber-flavored flowers, and I heard that if you *really* have time on your hands you can freeze them into ice cubes.

Sweet cicely is my most willing volunteer, but I welcome it because it scents the garden almost as well as the lavender. I pick my chard well into winter, but haven't seen it go to seed ever. You do need to be aware of cross-pollination and loss of some hybrid traits as well. Because of the intensive rotations I use only a few of my crops get to the seeding stage unintentionally, but in a permaculture setting it makes sense to encourage it.

yep. herbs. neighbor planted mint years ago, its effin everywhere now. i like it but only in his yard.

some flowers are notorious for it too. ive had potatoes keep popping up too, and usually feet away from where i planted. its like a present really

Dill will self seed quite well.

Mint I keep in a container because it's invasive.

Parsnips, Carrots, Arugula, Spinach, Broccoli, Beets I'm sure, etc.

I've had some self-seed that you wouldn't normally, out of a combination of curiousity and laziness. Chinese cabbage, tatsoi, tomatoes (they won't be true if you grew hybrids or had multiple varieties) are the ones that come to mind that haven't been mentioned yet. But I don't know that you would want those in the same space year after year. Oh, and bronze fennel. But that's another one that really becomes a weed, better to clip the flowers after the seeds start forming unless you want some fennel seed for the kitchen.

Thank you for all of the ideas. I will begin developing my areas for these experiments this weekend, if the wind dies down here.

I tried to allow Borage to self-seed but my season must be too short. They did not grow quickly enough to give me flowers before the first frost. I have not decided if I am enamored of it enough to start seed for it every year.

My arugula has seeded itself a couple times over, and gives me more than I can use. Same deal with oregano - the seeds must blow in the wind because not only does it come back in the same place every year, but every year, I find it coming up through the cracks of all areas of my backyard brickwork, where only the tiniest amount of soil resides. I never much cared for the flavor of oregano, of which I had only ever had in its dried form, until I finally gave in and ate some fresh stuff from the yard. Now, when it's in season, I chop it up and eat it with whatever I possibly can.

Dill, basil, cilantro, garlic chives, and New Zealand spinach for me.

Indeed, the red russian and other brassica napus cultivars are the supreme brassica self-sowers because they do not cross with the many brassica weeds.

I would offer tomato's sounds odd though, but in my old garden I grew a variety called Matt's Wild Cherry self
seed for about 4 seasons before i moved. The plants spread out and produce small 1/2" tomatoes. you'll never get them all...

Lettuce is my favorite self seeder. Cilantro and dill are heavy self seeders too.

Almost anything you let go to seed in the garden will self seed. Mine include squash, tomatoes, radish, dill, redroot, lambsquarters, kochia, dill, cilantro, cantaloupe, purslane, water grass, purslane, onion bulbs (missed a few when digging), purslane, spinach, lettuce, carrots. All I want to seed are the dill and cilantro. Just make sure the seed gets on the ground and gets worked in to a planting depth.

I have a thick carpet of parsnip seedlings on the path. They germinate infinitely better if self-seeded.
Lettuce, rocket and upland cress.
Calendula. And you thought borage was prolific!
A bit of a different situation, but every season I have pumpkins appear from the compost.
Chervil. Everywhere.
Phacelia. Ditto.
Salsify. Popping up all over the place.