Verbena bonariensis planted with orange cosmos sulphureus (tall combo)

California poppies -- mine have been blooming non-stop and producing seeds on the spent blooms.

Larkspur -- spring

Cornflowers-- 'Red Ball' is great IMHO -- lasts May-June with deadheading, but let some go to seed

nigella (I have extra seeds to share) -- get one plant to bloom and you'll never be without seeds. May bloom. interesting seed pods after.

rose campion

shasta daisy 'Alaska'

perennial ageratum -- seeds and spreads in moist areas

echinacea 'Prairie Splendor' seeds are easy to germinate and quick to bloom

nepeta 'Six Hills Giant' -- big plant; divide or seed

rudbeckia 'Goldsturm' -- buy one plant and it reseeds like crazy. Not my fave, but it's a filler.

monarda - buy one plant and it spreads. I like 'Blue Stocking', 'Raspberry Wine' and 'Jacob Cline'

bog sage - buy one plant and it spreads

salvia nemorosa 'Caradonna', 'Marcus', 'Sensation Rose' -- will produce seeds like parent

amsonia hubrichtii (blue star) -- great native plant for 3 seasons

platycoden (balloon flower) -- don't move the seedlings after they are a few inches high.

crepe myrtle 'Tuscarora' -- I find babies all the time! Blooms watermelon color.

baptisia -- you may get more than you want, so be sure to control the seed pods

bronze fennel -- be very careful. you can get thousands of seedlings in one year.

linaria 'Canon J Went' - should be able to pull the extras. pink

linum narbonense 'Heavenly Blue' (flax) -- my absolute favorite reseeding perennial.

I have a link on the left side of my blog where I show photos and list flowers that I grow from seed. I don't have all of these up there yet. Also, I wrote about affordable coneflowers with bee balm (below).

Cameron

Here is a link that might be useful: An Affordable Flower Combination

Momtoedna..if you're feeling brave and have lots of room you might try datura. Boy does it reseed nicely even when you think you've clipped off all the seedheads (which are round and prickly and then dry and split open dropping seeds but not flinging them).
It is related to brugsmansia (angel trumpet flower) but it blooms at night,very fragrant with a blossom that looks like a moon flower but on a sturdy branched plant instead of a vine.
Unlike brugsmansia, datura is very drought hardy and will seed where conditions suit it best. Mixed in with tall zinnias and verbena bonarensis(sp) for daytime color,the white fragrant blossoms really pop with brightness in the early evening through the early morning.

If you go back to the Southern forum and read that long thread on "plants you wished you'd never planted" you may find ideas for plant materials that spread happily in your large area that others didn't like in smaller beds.

You might also want to check into the wintersowing forum here. I also had a lot of space and practically no budget 5 years ago. Now it's almost maxed out, mostly due to wintersowing. Not only do you get lots and lots of little seedlings to plant out in spring, those nice folks over there are incredibly generous about sharing seeds with newbies.

It's a little more controlled than letting the reseeders have at it (although that can be fun) and you have a really enormous choice in plants.

Rhonda, check out the Carolina Exchange forum. They're not all posted yet, it's too early, but if you can make it to some of the fall plant swaps you'll fill those beds in no time with a wide variety of plants! There are also some seed swaps in the winter, then another round of plant swaps in the spring! Gardeners are very generous and love sharing with others!