You've already listed 2 of my three favorite companies (Johnny's Select Seeds and Baker Creek), so here's the other company in my top 3:
http://www.anniesheirloomseeds.com/
One of the things we bought from Annie's last year was heirloom potatoes. They performed great, even in our clay soil. We saved most of them for replanting this year. But, the few we indulged in eating were fantastic.