Tangoarizona:
A central reference for tango dancing in Arizona.
Phoenix Yahoo Group:
The Phoenix area tango discussion group.
Tucson Yahoo Group:
The Tucson area tango discussion group.

Technique

Oscar Casas:
A great collection of instructional youtube videos for the intermediate tango dancer.
General Lead/Follow:
Lead/Follow for Ballroom, West Coast Swing, etc. Much of it is applicable to tango.

Learn About Tango's Essense

Planet Tango:
Various articles about tango.
Tango and Chaos:
Articles about tango and its history, some tutorial and some videos. Sections 2 and 4 are very good.

Other Tango Links

Tejastango:
Links to extensive tango-related, annotated lists. This site has videos, music, a glossary and articles.
Tangozone:
Articles about tango and tango related health articles.
Tango L:
An international e-mail discussion group about tango.