Collect Britain is a free digital collection of over 90,000 images and sounds from the British Library's holdings. The items chosen all relate to Britain in some way (British music, photographs of British people, etc) and seems to be intended for both serious researchers and those who just want to browse through British visual and auditory history.
They have organized this collection in an easily navigable and interesting ways. One of the most diverting search tools I came across was an interactive map of Britain. You could choose a place on the map and it would show you all of the items related to that area. Images are always presented in thumbnails, and oftentimes you can hover the mouse icon over the thumbnail to get a magnified view. They also allow you to create your own personal collection by adding your "favorites" to a personal folder.
The parts of the collection that I found fascinating was their collection of accents and their currently highlighted collection of "Expressions of Faith" where they "invited a group of well-known people from different faiths" to choose their favorite images from the collection and write about their reflections on their religion.
The items to be included in the collection were chosen by the library's curators and digitized by their photography studio specifically created for this project. It was funded by a grant from the British government called the "Government's new opportunities fund". They sourced out the creation of their content management software (which is really what has set this project out from the others I have looked at previously) to the company System Associates and the design was similarly outsourced to specialists (Dusted Design Partners). For their metadata they used an extended version of Dublin Core (DCMES). They provide even more technical explanation of the aspects of the creation of this collection on their "about" page on the website.
The image quality is amazing and the advanced search tools are quite intuitive and easy to use. I definitely recommend taking a look at it.