CC, Nichols is great. I like Territorial seeds in Cottage Grove, Oregon nalso
www.territorialseeds.com
Heirloom seeds. Be sure to purchase heirloom varieties when possible, they will always be the highest quality, perfect for preservation and seeding the next generation. Heirlooms are quite interesting, I was looking at heirloom tomato varieties, and I came across one that was grown back in the days of George Washington, pretty cool. I don't have any specific companies to recommend, as I am also searching for the best source, but I know that I'll be buying heirloom.
seeds of change has got some kind of 100 million seed giveaway... you just pay the shipping (4.99) and receive 25 packs of seeds.
http://seedsofchangefoods.com/sowingmillions/sowingmillions.aspx
keep it green