I have chcked out Baker Creek Seeds and Seed Savers, but does anyone in my zone have ideas for other good seed companies?
I have bought exclusively from Baker Creek for 3 years now and have been very happy with them.
Botanical Interests has decent selection of heirloom varieties, nothing like BC or SSE but not too bad. I buy a lot from them because they have a good product and they are local (to me).
I'm not in your zone, but you might consider:
Fedco Seeds. They're in Waterville ME, which is 5a, but plenty of places in Maine are 3-4 (though folks like me from warmer areas buy from them also). They stock more than solely heirlooms, but I'm sure you'll find plenty to like on their list.
Johnny's Selected Seed is in Winslow ME (also 5a). They're less into heirlooms, but still a good source.
I'm in zone 5b in Missouri. Baker Creek is a little south of me in zone 6. I really like Sand Hill Preservation Center in Iowa. I don't know his zone but I suspect it a zone 4. He has all heirloom seeds. He doesn't do internet ordering. You need to send him a check in the mail. He's a little bit slow since he's a mom and pop company. He gives you great value for your money and has a good selection of varieties.
I also know of Southern Exposure Seed Exchange in Virginia but haven't ordered any thing from them.
You might consider Sandhill Preservations.
Here is a link that might be useful: Sandhill Preservations
I consider each of the following sources to be reputable sources of seeds and knowledge - I have gotten more reliable seed (true to description and germination) from all of these over Baker Creek over the years. Baker Creek has a great catalogue but the seeds have not lived up to hype too many times for me - lousy germination, not true to type. If I see something I am interested in - I source out from the places below:
Tatiana's Tomatobase Seed Shop - in BC - addicting with infoto learn/pics to drool over/common and rare heirloom seed (you've been warned)
Heritage Tomato Seed in CA - great guy, great seed - tomato porn pics - VSFW LOL
Sand Hill Preservation in IO - love what they are doing - they have all vegies and slips! Be patient with them
Gleckler Seedsmen - in OH - another family who is doing this in addition to their day jobs and families - awesome tomato seeds, pepper and a bit more
Mariannas Heirloom Seeds - in MI now (was in TN) - enthusiastic with awesome variety
Victory Seeds in OR - solid folk with good seed
Southern Exposure Seed Exchange - in VA Awesome dedicated folks with broad variety of all vegetables
The Sample Seeds Shop - in NY.Great variety of heirloom tomatoes, peppers, basils in smaller units; very reasonable and great germination.
Seeds from Italy - in KS Awesome source for Italian vegies - fantastic prices and germination
Tomatofest in CA - sort of like Vegas for heirloom tomatoes - glitzy and oh so good
Tomato Growers Supply - in FL (these are the folks who developed Black Cherry - no chit!) awesome for all members of nightshade family
For heirloom tomato: tomatofest.com; always good germination.
For various other seeds: sustainableseedco.com; good germination.
For some heirloom (they carry hybrids too so need to check plant by plant basis): mvseeds.com; good prices, but occasional inconsistency with seed quality (germination) and labeling mix ups expected.