I'd like to make some more specific places in Ann Arbor. It's such a fantastic place. They have graffiti alley (google it!!) which is constantly changing and is a PERFECT location. I'm planning on going there in the summer. As well as some old historical buildings on the University of Michigan campus, as well as ivy covered buildings (great for HP and other things), quaint houses, modern buildings, busy streets, empty streets, empty creepy alleyways. It has a cute little downtown near the campus.
Also, Frankenmuth. It's such a themed town. It feels super German and could be perfect for Hetalia, Princess Tutu, and others. The buildings are so picturesque, and they're meant for pictures since it's a touristy town.