Placemat - Pretty nice placeholder images.
Detour - Immersive audio walks, now in 17 cities
PlaceKitten - Dead-easy placeholder images. Of kittens.
Instalist - The most Instagrammable photo spots around the world 📸🌎
placeholder.pics - Lightest way to include placeholder images in your design
Urban Walks - A nicer way to explore New-York