Images
- HDRI Haven - 100% Free HDRIs, for Everyone
- pixabay - beautiful free images
- pexels - Best free stock photos in one place
- Unsplash - Beautiful, free photos
- Flickr - Open Source Photostream
- Unsplash - Beautiful, free photos
- https://www.europeana.eu/
- https://www.jamendo.com/
- https://openclipart.org/
- https://commons.wikimedia.org/wiki/Main_Page
- http://ccmixter.org/
- https://stocksnap.io/
- https://burst.shopify.com/
- https://www.foodiesfeed.com/
- https://gratisography.com/
- https://negativespace.co/
- https://freestocks.org/
- https://picography.co/
- https://mmtstock.com/
- https://skitterphoto.com/
- http://www.lifeofpix.com/
- http://littlevisuals.co/
- https://deathtothestockphoto.com/
- https://picjumbo.com/
- http://imcreator.com/free
- https://nos.twnsnd.co/
- http://jaymantri.com/
- https://kaboompics.com/
- http://epicantus.tumblr.com/
- https://shotstash.com/
- https://styledstock.co/
- http://www.publicdomainpictures.net/
- https://magdeleine.co/license/cc0/
- https://www.oldbookillustrations.com/
- https://isorepublic.com/
- https://publicdomainvectors.org/
- http://www.1millionfreepictures.com/
- http://www.freestockphotos.biz/
- http://realisticshots.com/
- http://startupstockphotos.com/
- https://www.flickr.com/photos/britishlibrary
- http://publicdomainreview.org/
- http://viiintage.wpengine.com/public-domain-images/
- http://publicdomainarchive.com/
- http://jeshoots.com/
- http://www.designerspics.com/
- http://www.everystockphoto.com/
- https://www.flickr.com/photos/spacex/
- http://fancycrave.com/
- http://creativevix.com/index
- http://barnimages.com/
- http://snapwiresnaps.tumblr.com/
- http://highresolution.photography/
- https://www.freeimages.com/
- https://www.shutterstock.com/search/open-source
- http://www.publicdomainsherpa.com/ - Copyright info
- https://thepicpac.com/ [paid]
Sound and Audio
- https://freesound.org/
- https://archive.org/details/audio
- https://archive.org/details/opensource_audio
- https://archive.org/details/librivoxaudio
- https://archive.org/details/etree
- http://freemusicarchive.org/
- http://opsound.org/
- http://soundbible.com/royalty-free-sounds-1.html
- https://soundcloud.com/nasa NASA on Soundcloud
- http://99sounds.org/
- http://www.noiseforfun.com/
- http://incompetech.com/music/
- http://raisedbeaches.com/octave/
- https://musopen.org/
- https://www.playonloop.com/
- https://www.bensound.com/
- https://www.soundjay.com/
- http://dig.ccmixter.org/free
- http://www.soundgator.com/
- http://www.pacdv.com/sounds/index.html
- http://www.freesfx.co.uk/
- http://www.audiomicro.com/
- http://www.grsites.com/archive/sounds/
- https://www.youtube.com/audiolibrary/music
- http://sounds.bl.uk/Information/Audio-Tools/
- https://www.nasa.gov/connect/sounds/index.html
- https://www.partnersinrhyme.com/pir/PIRsfx.shtml
- http://www.soundcities.com/info.php
Digital Assets
More Categories to come...