Came across notfound.org an organization that is trying to help find missing children.
What they do is partner with individual web sites to replace the 404 not found page, with a photo of a child that is missing. This happens automatically via a plugin of sorts.
Aside from the mission, I love the creative use of wasted web space. Finding what is considered relatively useless for most people (404 page) and changing its function to make it inherently useful is commendable.