The Mockup Club is a free-mockup site built by Olivier Heitz, offering quality-checked, up-to-date product and packaging mockups vetted to be free of spam or malware.
The explicit quality-checking (a real point of difference from open-upload freebie sites), means less time wasted on broken smart objects or low-res files.
Good for product and packaging presentation specifically: its catalog leans more toward physical products than app/web UI mockups.
It's a smaller, single-curator catalog rather than a massive aggregator, so depth in any one product category is more limited than a site like Freebiesbug or Good Mockups.
Free design mockups, curated and ready to use.