Built St. Louis - A site dedicated to the historic architecture of St. Louis, featuring lots of information on abandoned buildings.
Ecology of Absence - Not just a good collection of trip pictures, but a good collection of thoughtful writing on the subject of the "biocultural geography" of abandonment in Saint Louis.
Sonic Atrophy - Nice photos and write-ups relating to abandoned buildings in and around St. Louis.
Underground Ozarks - An excellent site featuring photo galleries and a regularly updated blog related to a variety of locations in southwest Missouri and beyond.
Urban Ninja Force - A nice looking site from a ninja-obsessed group of tunnels, drainers and abandoned building explorers operating out of Springfield.