North America

Cereal Trespassers
Urban exploration photo gallery.
http://www.cerealtrespassers.net/

DK Photo Group
Group of photographers who post their urban exploration photographs. US and Canadian locations.
http://www.dkphotogroup.com/

Lost America Night Photography
Troy Paiva's collection of night photography of the abandoned roadside west.
http://www.lostamerica.com/

Tribe: Building Hacks
Forums about forms of urban exploration. Using urban settings in non-conventional ways.
http://url-word.tribe.net/

Urban Exploration Mexico
Photoblog with some write ups about explorations in Mexico.
http://abbandonedplacesmexico.blogspot.com/

Urbanized
A collection of photography by Robert Stephens focused on urban decay and the urban landscape in general.
http://www.urbanized.net/