Video Downloaders:
Still Images
HyperAllergic article on the NYPL’s release of digital archive, with links
Lots of National Geographic images: natgeofound, vintage National Geographic, scanned vintage National Geographic
Pixabay: Free high-quality images you can use anywhere
Pixnio: more free public domain images
The Getty’s Open Content Program (great for vintage photographs)
Lost and Taken (free textures)
Textures.com - many free textures, but you do have to at least have a free account with them to download anything
deviantart - also a good place for textures
Audio:
incompetech - composer Kevin McLeod has a large archive of music that's free to use with attribution.
Stills, Audio, and Video - 1-stop shopping!
Internet Archive - A huge collection (actually a collection of many collections of media), all free and public domain
Brushes & Fonts:
From Jessye :)
200+ brush set (Illustrator only)