Mockuuups Studio - Fast and easy way to create product mockups on macOS, Windows and Linux.
Facebook Design - Devices - Images and Sketch files of popular devices.
Placeit - Generate realistic product shots in seconds
Smartmockups - Create stunning product mockups, easily and online.
Mediamodifier - Create beautiful designs and product mockups in seconds.
mockDrop - Is a webapp for creating free device mockups including your screenshots.