I placed an order to the Sand Hill Preservation Center today. Let me give you the scoop on this wonderful seed source. The main goal of the owners is to preserve our genetic resources. They offer heirloom poultry, seeds, and sweet potato slips. (Over 90 kinds of sweet potato slips.) The cover of their catalog states that they offer "over 1400 rare and genetic treasures." This is one of the cheapest sources for heirloom vegetable seeds. Bonus- if you order $10 or more there are no shipping or handling charges!
There is a website, but Sand Hill only accepts mail orders. (Glenn Drowns, the owner, says that he will accept internet orders when he can ship seeds and poultry over the net.) You can view the catalog and download an orderform at the website. They do not accept credit cards, only check or money orders. Read the About Us section carefully, the Drowns have full time jobs in addition to the Center, so there may be up to a 3 week turnaround on seeds during peak season. Still, it's worth it. These are people of integrity doing good work.