UER - Urban Exploration Resource
Urban Exploration - as defined by Wikipedia
Infiltration - The site that in my opinion gave explorers a definition for what they do.
Texploration.org - A great site by a long time exploring buddy, Noah Vale.
Urban Alexploration - This site has tons and tons of Texas underground stuff and plenty of other good stuff.
Barry Kooda - Barry Kooda's website. You can find the UE stuff under "photos". Don't forget to check out the MP3s though.
UETX.com - Based in The DFW area but quickly beginning to explore everything within reach.