PlaceKitten - Dead-easy placeholder images. Of kittens.
Videvo - Free HD stock footage & motion graphics for any project!
PlaceIMG - Placeholder images for your project in progress. Custom URLs generate placeholder pictures in various sizes with categories and effects.
Mixkit - High-quality stock videos that are completely free.
Placehold.co - Placehold.co is a placeholding website that lets you create your desired template for image placeholding.
Mazwai - Find and download the best HD videos under Creative Commons.