My favorite digital collections site is from Duke University Libraries: library.duke.edu/digitalcollections/ Beautiful design and so easy to dive effortlessly into the content.
I usually hate seeing social media on digital collections pages, because how disheartening to see 0 likes, 0 tweets, 0 comments on most of your items. But for promoted collections, like their Historic American Sheet Music, I was surprised and impressed to see some community participation.
I wonder how they assign subject headings. Some look like LCSH (abundance of dashes) and some seem more like tags. The subjects link to other items in their catalog, which is useful, although it takes you out of the Digital Collections site experience.
According to their About page, the application was built in-house using Django and a good number of tools and widgets. (I usually use BuiltWith to get a behind-the-scenes peek at a site’s architecture.)
Well done, Duke!