fishtown in queens (northern blvd). rating from 1 to 10 i give it a 7. prices are ok, although they have been rising recently. on a good day you will find a good selection of fish. i believe the best days are mondays. as for corals they don't have much at all.
there's also new world aquariumin manhattan(38th + 2nd ave). rating from 1 to 10 is an 8/9. a bit pricey. on a good day you will find tons of fish(large,small,reef safe,non-reef safe), smaller invert tanks, several tanks of corals. but like i said before pricey.