Images & media
The following sites offer royalty-free media. Some require attribution, others do not.
Sites that contain different types of images (pictures, illustrations, icons, etc.)
https://gratisography.com/ (Unique images! It could be great for creative writing)
https://www.photosforclass.com/ (school-appropriate images pulled from Flickr and Pixabay)
https://www.pics4learning.com/ (free photos for education purposes)
https://commons.wikimedia.org/
http://www.scola.org/Default.aspx (their "World Photo Gallery" has over 32,000 images; also world TV & periodicals, and interactive lessons in various LCTLs)
"Culturally Authentic Pictorial Lexicon" (collection of authentic photographs arranged by language and context)
The "Realia Project" (a collection of images from around the world, but no longer maintained, so the images might be outdated)
Clip art & icons only
Open Clipart (clip art only)
Flaticon (icons)
Also available as a Chrome extension
SVG Silh (icons, SVG files)
Health Icons (icons related to health only)
The noun project (icons only; great for infographics, flyers, etc.)
https://handdrawngoods.com/freebies (hand-drawn icons)
https://www.iconsmania.com/ (free, editable icons)
Blog post explaining how to create your own icons using AutoDraw
Visuals for Developing Communication Skills in Foreign Language Classes (drawings)
Audio / Videos
https://www.youtube.com/audiolibrary/ (free music and sound effects)
https://www.nextvista.org/ ("Next Vista For Learning" provides a library of free videos made by and for teachers and students)
https://www.classhook.com/ (educational videos from TV shows and movies to use in your lessons)
https://langmedia.fivecolleges.edu/language-by-country (videos done by international students in their home countries; available in these languages: Arabic, French, German, Spanish, Japanese, Greek, Italian, and Portuguese)
https://www.audio-lingua.eu/ ( mp3 recordings in 13 different languages, which can be downloaded or embedded)
https://commons.wikimedia.org/ (video and audio files, in addition to images)