Here are some of the best free resources I’ve found for branding and product mockups.
1. Good Mockups
Good Mockups offers free PSD files for designers.
2. Graphic Pear
Graphic Pear offers free and premium distinctive mockups, fonts, templates, icons and other resources for designers.
3. Mockup World
Mockup World handpicks and presents the best photorealistic Photoshop mockups that designers and agencies worldwide have published online.
4. Mr. Mockup
Mr.Mockup helps creative professionals to showcase their work in the best way possible.