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.
Open Peeps
Need something a little more hand-drawn? Open Peeps is the illustration library for you. Created by Pablo Stanley, the open-source flat SVG and PNG assets are available for Sketch, Figma, Studio and XD. You can even make a donation if you’re able to support Pablo. A little goes a long way.
unDraw

Describing itself as “open-source illustration for any idea you can imagine and create”, unDraw is a constantly updated design project by Katerina Limpitsouni featuring beautiful SVG images that you can use completely free and without attribution. We particularly love the ability to quickly add your own hex code to tailor the illustrations to your own projects.
humaaans

Mix-&-match illustrations of people with a design library In Humaaans, Pablo Stanley has created something quite special: modular, vector illustrations of humans that you can mix, match, rotate and position to create your own designs. Whatever you make is free for both commercial and personal use.