AquaTek is a good place for more unusual freshwater fish. Very healthy fish, a decent little saltwater selection, and I love the freshwater selection.
Not only do they have some of your basic fish like several kinds of cories and tetras and some nice bigger-ish fish like angelfish, they have more unusual-ish things like pygmy cories, marbled hatchetfish, algae-eater gobies, a few brackish species, gudgeons, and halfbeaks. That's just a tiny list of what they have.
They also have 'saltwater tadpoles', AKA clingfish gobies, on a regular basis.
Another bonus is that they get bluefin killifish and swamp darters in with their ghost shrimp shipments every now and then, so if you're lucky you can pick up one of those unusual fish for something like two bucks.