Yes. Itch.io. Have you seen how much free art to use in games is right here?!
Further than that it depends on your game and what kind of art you're looking for.
Other sites you need to be careful that they allow commercial use - that's normally indicated somewhere on a legitimate site. If you publish the game, it's not personal use - it's commercial use even if you don't charge for it.
You can find free art at Pixabay. - they indicate next to each picture whether it's free for commercial use or not.
Renderosity also has a huge free stuff section - they also show beneath each picture whether it's allowed for commercial use.