A couple newer ones around Detroit that I didn't see listed:
UHF Music
Royal Oak
-Good selection, great staff, decent pricing. Mostly used but good, relevant new stock as well. Used selection is very diverse for how small the overall size of stock is. Found Sound
Ferndale
-About the same as UHF except I think they've got better prices overall. The staff is as or more friendly than UHF and have been very helpful in the few visits I've made.
Dearborn Music
-This one has been mentioned already but I wanted to throw another plug out there for them. Excellent store with great owners and great staff!