Interfacer - Collection of more than 200+ free design resources
Humaaans - Mix-&-match illustrations of humans with a design library.
Blush - Illustrations for everyone
Control Illustrations - 108 free flat illustrations with customizable characters
Freebiesbug - Collection of the best free web design resources.
Ouch! Illustrations by Icons8 - Professional, perfectly matching, and customizable illustrations for any designs