Design Cell - Beautiful multipurpose mockups for iOS
Ouch! Illustrations by Icons8 - Professional, perfectly matching, and customizable illustrations for any designs
Facebook Design - Devices - Images and Sketch files of popular devices.
Control Illustrations - 108 free flat illustrations with customizable characters
Device Shots - Generate high-resolution device mockups using a screenshot.
Humaaans - Mix-&-match illustrations of humans with a design library.