Le Jardin du Gourmet, out of Vermont. I'll also put a plug in the Green Pages (although frankly I find that less useful since we are only allowed to submit positive reviews). Anyway, I've ordered from these folks several times, and have always had good luck with germination. They sell in either sampler packs (5-10 seeds for about 40 cents) or regular packs. For me, I love to just get the samplers so I can try new varieties each year without breaking the bank or worrying overmuch about keeping seed fresh for future years. Since I'm now planting for two people, I only really need or want one hill of zukes, one of pumpkin, etc. The sampler packs come in little b/w paper envelopes about 2x3" big with just the name stamped on - no frills but the price is right. In addition to veggie seeds, they also offer herb and flower seeds, again in two sizes.
Their web site is http://www.artisticgardens.com