The Society for the Preservation of New York City Manhole Covers (Location has changed several times, and is once more defunct; once http://www.nycmanholecovers.org, http://pearlstreetrevival.typepad.com/nycmanholecovers, http://home.earthlink.net/%7Ebeautyunderfoot/, etc)
Scottish Ironwork -
"scottishironwork.org is the world-wide focus to celebrate the
Scottish ironwork tradition. It is an exciting resource that
provides information for those interested in wrought and cast
ironwork manufactured or found in Scotland. On this site you
will find historical information, an online database, technical
area and special features."