Theme Forest - The #1 marketplace for premium website templates, including themes for WordPress, Magento, Drupal, Joomla, and more. Create a website, fast.
Device Shots - Generate high-resolution device mockups using a screenshot.
ThemeFuse - ThemeFuse is a store that provides high-quality designed WordPress themes to let you stand apart from the crowd.
Facebook Design - Devices - Images and Sketch files of popular devices.
ThemeGrill - ThemeGrill is an online marketplace that develops and sells WordPress themes and plugins that you can buy to create professional websites for businesses, magazines, and blogs.
Mockuuups Studio - Fast and easy way to create product mockups on macOS, Windows and Linux.