some common varieties we like... (we've been growing them for 9 years, in similar climate to you).
orange banana (for flavor) they are a little picky and they split sometimes, but they taste great
Black krim - nice "black" beefsteak type, tasty, decent yield
green zebra are popular, yield well, nice visuals, decent taste
for little tomatoes...
riesentraube gelf
black cherry
white currant have a unique flavor profile if you want a small tomato
green grape also have an interesting taste
I like to have a white one too for color, but I can't remember which variety was best for taste.
then there's the classic Brandywine if you want a plain ole beefsteak type
and others for sundried or sauce
I have since lost the seed, but we grew one called Watermelon Beefsteak that we enjoyed for huge tomatoes.
joining SSE is a nice idea, we got some good varieties from a private collector who had an unbelievable collection. We've also got them from Baker Creek in the past
Baker Creek Heirloom Seeds - 1000 Heirloom Garden Seeds in our Heritage Seed Catalog, Historic Gardening Shows and Plant Festivals, they give decent quantity I haven't tried Marianne Jones, sounds like a great source.
Have fun!