Cold War Shooters is starting to build up. They're on N. Mesa, next to a pet grooming place. It's pretty hard to spot, and they don't really advertise that they're there. They have tons of AR15 stuff.
Sun City Guns on Montana is pretty good. Selection can be somewhat limited but the staff are really knowledgeable, can order what you need if they don't have it and are a Class 3 dealer so NFA items are no problem as well. I have always had good luck there but just my 2 cents.