Agreed, Preuss Pets is amazing. Prices abit high, but the selection, quality, and knowledge of the place is astounding.
Also, check these places out:
Fantastic Fins in Livonia. Tons of Dwarfs, LOTS of "real" monsters. Arowanas, Plenty of Rays, FHs, Dovii, Jags, Wild Caught almost everything.. from Festaes to Celestial Pearl Danios. They had a 1foot deep 3 foot long Arowana the other day, it was amazing. The staff is unbelievable in their knowledge, and is more than willing to help anyone out. Not a big selection of plants or equipment, but they have about 10 kinds of live food, and ALOT LOT of harder to find species in almost everyday. Only place I've found in MI that offers alot of Apistogramma, Corydoras, Rays, etc. One of the owners has bred something like 350+ species, so he knows his stuff, especially when it comes to Plecos.
Something Fishy in Westland. Great prices on everything. Large selection of equipment, lots of tanks, and clean. Knowledgeable staff for the most part, sometimes pushy if you browse a long time like I do. But, prices are too good to pass up, and they have quite a few "monsters" as well.
Also, if Cichlids are your thing, the Oyer's house is in Brighton. They're top-notch Cichlid breeders who have turned their house into a farm. The garage, basement, and most of the house, are filled with tanks with fish for sale. Call them and ask for a tour, they're pretty friendly people.