Magic Pet Shop is a mom and pop store in Wethersfield on the Silas Deane Hwy. Very small, but very healthy selection of fish, and low prices on tanks/stands/etc. Never had a casualty from them.
One place to avoid is Exotic Fin and Feathers in East Hartford. The place is big, with a nice selection, but they overcharge, and their fish are really not very healthy.
I've been to Magic Pet Shop before and I really didn't like the place at all. They had puppies and birds in the back and there were flies all over them. The price on some fish was pretty decent. I recommend Aquatic Wildlife in Manchester if you're looking for exotic fish.