Where to find free art (without using generative image models)

[Jubal]

There's actually quite a lot of places online where you can get free resources for your projects via Creative Commons licensing or public domain works. Here's a list of some places you can find such things! Additions/submissions welcome.

3D Models

Open Game Art (3D Section)
Large site full of Creative Commons licensed artworks for games.
Link: https://opengameart.org/art-search-advanced?keys=&field_art_type_tid%5B%5D=10&sort_by=count&sort_order=DESC

2D Images

Old Book Art
A largish collection of CC-0 art plates from old books, maintained by a bookshop owner from the US.
Link: https://www.oldbookart.com/

Old Book Illustrations
A site focused on Victorian and French Romantic book illustrations, all of which are public domain.
Link: https://www.oldbookillustrations.com/

Open Game Art (Concepts & 2D)
Large site full of Creative Commons licensed artworks for games. Focused on game art and including e.g. animated 2d artworks.
Link: https://opengameart.org/art-search-advanced?keys=&title=&field_art_tags_tid_op=or&field_art_tags_tid=&name=&field_art_type_tid%5B%5D=9&field_art_type_tid%5B%5D=7273&sort_by=count&sort_order=DESC&items_per_page=24&Collection=

Internet Archive Book Images
A pro tip for this resource: Flickr's search is quite janky, and it defaults to unselecting illustrations. So if you're not seeing any search results when searching within the resource, check the advanced tab and make sure that illustrations are properly selected.
Link: https://www.flickr.com/photos/internetarchivebookimages/

Wikimedia Commons
A large resource - most files are creative commons but not necessarily CC-0, so make sure you check the licensing. On the other hand, much more by way of photography and up to date art than some other options here.
Link: https://commons.wikimedia.org/wiki/Main_Page

Textures

Open Game Art (Textures)
Large site full of Creative Commons licensed artworks for games.
Link: https://opengameart.org/art-search-advanced?keys=&field_art_type_tid%5B%5D=14&sort_by=count&sort_order=DESC

SoundImage Texture Library
A very large collection of basic texture images for stone, metal, wood, paper, etc. See also the creator's Exilian thread for updates.
Link: https://soundimage.org/images-home-page/

Sound Effects

Open Game Art (SFX)
Large site full of Creative Commons licensed artworks for games.
https://opengameart.org/art-search-advanced?keys=&title=&field_art_tags_tid_op=or&field_art_tags_tid=&name=&field_art_type_tid%5B%5D=13&sort_by=count&sort_order=DESC&items_per_page=24&Collection=

SoundImage SFX Library
A large collection of basic SFX.
Link: https://soundimage.org/

Music

Open Game Art (Music)
Large site full of Creative Commons licensed artworks for games. Tends to focus on quite "backgroundy" music.
Link: https://opengameart.org/art-search-advanced?keys=&field_art_type_tid%5B%5D=12&sort_by=count&sort_order=DESC

SoundImage Music Library
A huge collection of background music for all purposes. Useable in all projects with attribution. See also the creator's Exilian thread for updates.
Link: https://soundimage.org/

[JessMahler]

Pixabay is another good one for 2d images
https://pixabay.com/