I always recommend cheapseeds.com to newbies. It's great for basic flowers, huge amounts of them, cheap, and free shipping. They just don't have the fancy newer hybrids, but very good basics, excellent germination.
Swallowtail has become a favorite of mine. Decent seed counts, good selection, good prices, good germination rates for me. I also like Vesseys. Harris has a nice selection too, lots of pelleted seeds, but kind of pricey.
Karen