Musopen (classical music only)
Jamendo
SoundCloud
Internet Archive
YouTube Audio Library
Freesound (sound effects only)
In addition to these sites, there are also a number of independent artists who offer their music for free download on their own websites or through platforms like Bandcamp.
It's worth noting that while these sites offer free downloads, some may require you to create an account or may have other restrictions, such as limits on the number of downloads per day. Additionally, the availability of specific songs may vary depending on your location or the artist's preferences.