Mockup`s Design is a simple site where designers can find premium-quality free mockups, to use in their projects.
Facebook Design offers some of the best, high quality device mockups, UI kits, images and more. To be used by designers and developers for free.
Mockup Hunt is a huge collection of the best free mockups hand-curated from the most trusted mockup websites. Their collection is updated weekly.
Mr. Mockup offers free high quality Photoshop (PSD) mockups to showcase your design work like a pro!