You want to get heirloom seeds. These kind of seeds predate the early 1950s, predate genetically modified seeds. A GMO seed has been modified with genetic materiel from other plants and even animals such as fish. A GMO seed will grow fine, but using seed from that to grow the next crop might, or might not, get you the plant you thought you were planting, and the seeds might not grow at all. If you were trying to grow a pumpkin, you might wind up with a gourd, etc.
An heirloom seed is an unmodified strain that will get you that same plant, time after time. But unlike GMO seeds, it won't do well with many pesticides. If you have heard of a "Roundup ready seed" that is one that has been modified so Roundup will kill the weeds and not the crop. But that's more of a big farm thing than a backyard garden thing.
The other thing is, you ever bought a tomato that tasted like cardboard? GMO seed. Heirloom seeds don't do that.
There are some folks here in Arkansas that do this, been at it for the past year as a business. And they've come to our Tea Party meetings to speak on the subject as well.
http://hickoryridgeseeds.com/index.html