You can get a lot of heirlooms and organics from Heavenly Seed in Anderson, SC. Mike used to work at Clemson and ran SC Foundation Seed through the extension part of the school. Very nice seed quality.

http://www.heavenlyseed.net/

I like Southern Exposure seeds out of Virginia but I buy for the product not necessarily the company selling it - whoever has the seed I want gets my money. Nowadays I end up trading with other gardeners over the internet more than buying.

What are you looking for? The seed swap forum here has a lot of heirlooms for a swap or postage. I have several variates of heirloom beans and southern peas.

I order from Seeds Now, Sow True Seed (an Asheville company), Territorial Seed, and High Mowing.

I've ordered from Baker Creek and a couple other places, but my favorite is Fedco Seeds. Open-pollinated and heirlooms, and the cheapest prices I've found.

I learned about Sample Seed Company from Craig LeHoullier's (nctomatoman.com) website and new book, Epic Tomatoes. This company has a good but limited selection of heirloom seed most of which are in small packets selling for $1.50 & $2. If you want to grow a few plants of a lot of different varieties, this is the way to go. Germination was near 100% on everything that I planted.