trevorland.com Some great Arizona UE photos
Standing but not Operating Amusement Parks
Opacity Excellent site
Dead Malls Malls that have shut down
Lost America Night UE
Sutro Baths Excellent site on Sutro Baths in San Francisco
UER Urban Explorer Resource. Probably the best general UE site. Thousands of pictures worldwide.
Infiltration A UE e-zine Appears to be defunct itself, but still a interesting read.
Abandoned Russian Federation -- hasn't been updated since 2003
Reichs Autobahn Abandoned highway in Poland built during WWII
derelict london You have to dig around a bit to find the good stuff on this site, but there are some great pics and essays there.
Underground Kent Includes WWII and Cold War ruins.