These have bloomed and reseeded in my garden at one time or another.

Calendula--A medicinal plant that has been around for a long time. A salve made from the flowers is good for minor burns and cuts. It comes in an 18" or 12 " variety. Orange, Yellow and cream pom pom type flowers

Annual forget-me-not--there's a perennial too but it only blooms for a week or 2. About 12" to 14" tall with tiny masses of blue flowers.

Pansy--a very reliable self seeder.

Snap dragon--It is a slow grower but it comes up when the frost is coming out of the ground.

Annual poppies.

Zinnias and Marigold seeds can be collected and planted outside after danger of frost is past. They will bloom in about 1 1/2 months

You might also want to investigate winter sowing in these forums. It is a good way to grow a lot of plants when you don't have a greenhouse.

Verbena bonariensis -- reseeds to the point of extreme weediness, but it's a wonderful garden plant so I forgive it for making thousands, no, tens of thousands of seedlings.

I agree with both responders above. Also, rudbeckia annual varieties reseed vigorously. The rudbeckia, snapdragons, calendula and verbena all have normally been annuals, but the past winter was so mild that many of those plants survived and were up and blooming early this season. I also second the wintersowing recomendation. I've been doing it for years and it's an addiction in itself. And it's fun to collect seeds and trade with other gardeners, too. Good luck!

Martha

in my z5 i would add:

lychis.. rose campion
balsam
for get me not
annual poppy

and many, many annual weeds ... lol ...

ken

Some other annuals that I often fight unwanted volunteers include amaranth, Nigella damascena, Datura, bachelor buttons, and Persicaria orientale/Kiss Me Over The Garden Gate.

Ditto with feverfew and foxgloves, both technically biennial.

Thanks guys! This is so much fun. I love winter sowing too. The last couple of years I was rather non-functional since I had a newborn and my gardening activities all but ceased :-( Looking forward to getting into it again.

I have to agree about the Nigella, denninmi but I love them so. They are like little jewels.

I want to try some poppies for sure and the rose campion too.

I'm loving all these wonderful suggestions :-)

Amna

I used to garden in Z6 so am speaking from experience. The following can be added to the self-seeding list:

salvia coccinea
malva zebrina
cleome

Larkspur reseeds heavily for me, I haven't planted it in a couple of years, yet one of my garden beds is full of them. Others that reseed for me - california poppy, portulaca, snapdragon, pansies, cosmos, nicotiana, calendula.

Nasturtiums too.

johnny jump ups...

cornflower.. which was called bachelor button above ...

4 oclocks ...

moss rose if no mulch

allysum ... but 99% white.. no matter which color you planted the year prior ...

larkspur

will keep an eye out for others in the garden ..

ken

Just remembered these masses of Cleomes in a neighborhood yard. Looked stunning and the lady said that she has never had any issues with them coming back year after year. She very nicely offered that I could collect seed when the pods were ripe :-)

Amna

Black eyed Susan Vine? Thunbergia. I inserted a question mark because last year was the first time I tried them. I've seen many reseed, but it could have to do with the warm winter. Yes, I've noticed Cleomes will come back with vigor.