iStockPack offers a clear preview format so users can see the finished product and the vector file.
I love stock databases. They're the best marriage of sharing culture with graphic design, and they're a great resource for designers, especially ones working freelance or in small teams.
iStockPack offers a great resource for packaging nerds, filled with user-submitted content like a hexagonal cake box that looks like a starfish when opened to a complex series of interlocking cubes. Simple boxes, bags and wraps are also available. All the files I found are vectorized for easy manipulation, customization and remixing.
The site, still new, could use a few more resources, like clearer restrictions on licensing and usage. The usage section does mention restrictions, but it would be useful to include familiar language from, say, Creative Commons Licenses. It would also be great to have more social media features, to make it easier to share the ideas and inspiration on sites like Pinterest and Tumblr and to build a community amongst contributors.
But either way, iStockPack is a great pool of resources, and as they mention on their site, they're looking for more user contributions. Some contributions, like the ones below, offer extensive directions and resources.
This set of intersecting cubes uploaded by user ikarusmedia comes with extensive directions on assembling the finished product.