[asteram]

Most of the seeds you buy are not GMO. Very few plants have been messed with; the only vegetable that I know of that has been messed with is the tomato.

Corn, maize, has been GMOed a lot, but it's actually a grain not a vegetable.

The main danger from the GMO stuff is that it readily cross-pollinates and contaminates other non-GMO plants; there's a good chance that most of the corn/maize grown in the USA has been contaminated, as well as the soybeans. This holds true for organic crops too. The only solution I can think of would be to find heirloom maize seeds and grow them in an isolated area where they can't be cross-pollinated by GMOs.

Most garden seeds today are hybrids, which simply means that two parent plants with different characteristics have been crossed to give a plant with some desirable trait, such as yield, appearance, disease resistance etc. There is nothing inherently wrong with that; the only real drawback is that hybrids do not breed true. However, if two broccolis are crossed to make a hybrid broccoli, and that broccoli's seeds are saved and planted, you will still get some type of broccoli, and can select and gather seeds from those you like the best, starting your own improvement program. If all you can get is hybrid seeds, buy them. (usually they will be marked F1 or F2, meaning how many generations of crosses were made)

Heirloom seeds are an excellent thing to get, but I would recommend buying a few packs from the supplier and doing a germination test, rather than buying a bunch, putting them in storage, and finding out whether they sprout or not when you can't afford failure. I've had some poor experiences with commercial heirloom seeds, ranging from complete failure to germinate to a mixed bunch of week and weedy plants. All of the seed's energy and potential is contained in that tiny capsule; you want strong seeds.