Stock Photos:

Unsplash (free high-quality photos)

Pexels (free stock photos and videos)

Shutterstock (paid but offers a wide variety of options)

Stock Videos:

Videvo (free stock videos)

Pixabay (free videos and images)

Pond5 (affordable stock footage)

Stock Music:

Bensound (free royalty-free music)

AudioJungle (paid but high-quality music)

FreeMusicArchive (free legal music)