Local Projects is a New York based design firm that seems to be specializing in interactive maps. Looks like they've done a number of interesting projects, oriented around allowing people to annotate maps with their personal memories.
In my work on the Encyclopedia of Chicago History Online, I'm trying to spread the meme of letting all comers, through Web based authoring technologies, be able to annotate primary materials, including many of the historical maps that are going to be included. Seems like Local Projects has some lessons learned that might be valuable.