If we're just talking about the number of kinds of seeds offered (and no other factors), if we don't mean exclusively
tomato breeds, take a look at these stores, which have lots of stuff:
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Trade Winds Fruit (they add new stuff all the time, too; not just once a year; they probably sell more plant species than any other online seed vendor)
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Reimer Seeds
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Baker Creek
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Pepper Lover (loads of pepper breeds)
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TomatoFest
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Victory Seeds
I've shopped at all of those I listed, except for Pepper Lover. They've all been pretty good for the most part, but Baker Creek is my favorite among those (especially as you can find lots of reviews for a lot of stuff, and the reviews generally tell you the general location of the reviewer). Baker Creek is based out of Missouri.
I didn't relist any that people have already mentioned, but I agree that some of them have a whole lot of kinds of seeds.
Tatiana's TOMATObase Seed Shop does indeed have lots of varieties, but I thought I'd point out that it's a Canadian store (and ships from Canada); so, if you plan to order from the USA, in order to be legal about it, you'll need to get a Small Lots of Seed permit before ordering (they are said to be free, though). I would recommend ordering from somewhere with a warmer, humid climate like yours probably is, anyway, though (for your first store), although sometimes they get their seeds from breeders who grew them in other climates.
You may also be interested in
Southern Exposure (and although it has a good selection, I think the others I listed have more); I believe it's based out of Mineral, Virginia.
Tomato Growers Supply Company seems to be based out of Fort Myers, Florida.