I am really late to this thread having just noticed it in the newly merged Edibles and Preserving Forum. But the absolutly BEST selection of varieties is from TomatoFest.
http://store.tomatofest.com/
I like the way you can browse by season or by color or even more catagories. And they have varieties you just can not find anywhere else!
The second place I absolutely must mention is Heritage Tomato Seed. Mostly because I intend to get seed from some of the New Dwarf Varieties.
http://heritagetomatoseed.com/
Never heard of the New Dwarfs? They are from The Dwarf Tomato Project. Exciting news!
http://www.dwarftomatoproject....
I think these dwarf plants be a great addition to any garden but especially if one is low on space or for container gardens.
And just the greatest tomato resource out there on the net. Tatiana's Tomatobase! If you are interested in tomato varieties you have just got to take a look at this site.
http://t.tatianastomatobase.co...
