Imágenes de uso libre:
https://css-tricks.com/sites-with-high-quality-photos-you-can-use-for-free/
http://deathtothestockphoto.com/
Imágenes de stock:
http://www.istockphoto.com/
https://es.fotolia.com
https://creativemarket.com/
Video:
https://vimeo.com/
https://www.youtube.com/