High Mowing Organic Seeds is another great place to order seed. (although my heart will always be with St.Clare Heirloom Seeds.)In 1999 they created the Safe Seed Pledge to help spread the word and distinguish non-gmo seed sellers from the rest. Here is an article about that:

http://www.highmowingseeds.com/the-safe-seed-pledge.html

(this is the most concise well written description of this issue I have seen. It will take you less than 3 minutes to read it, and it’s very important.)

And here is the pledge itself (Taken off the St.Clare Heirloom Seeds web site):

“Agriculture and seeds provide the basis upon which our lives depend. We must protect this foundation as a safe and genetically stable source for future generations. For the benefit of all farmers, gardeners and consumers who want an alternative,

We pledge that we do not knowingly buy or sell genetically engineered seeds or plants.

The mechanical transfer of genetic material outside of natural reproductive methods and between genera, families or kingdoms, poses great biological risks as well as economic, political, and cultural threats. We feel that genetically engineered varieties have been insufficiently tested prior to public release. More research and testing is necessary to further assess the potential risks of genetically engineered seeds. Further, we wish to support agricultural progress that leads to healthier soils, genetically diverse agricultural ecosystems and ultimately healthy people and communities.”