Sharing two resources that I think are worth adding to this collection (if you're taking fan suggestions):
- Openverse: https://openverse.org/ - effectively a search engine that finds images and audio from loads of online resources and syndicates them into one place, with filtering for licence type.
- WordPress.org Photos: https://wordpress.org/photos/ - an always expanding repo of community-submitted photos that are all free to use under the CC0 licence (i.e. no restrictions).