storytale.io
Storytale is a subscription-based stock illustration site. But if you don’t want to pay, you can find a number of free illustrations here too, gathered together under the ‘Freebies’ tab. We particularly like their selection of vector illustrations for use on a 404 error page.
freepik.com
All the assets you need, in one place Find and download the best high-quality photos, vectors, videos, and mockups
elements.envato.com
pngtree.com
Royalty free png images, vectors, backgrounds, templates, text effect