The National Model Railroad Association is the largest organization devoted to the development, promotion, and enjoyment of the hobby of model railroading...
Lone Star Region, Division 6 of the NMRA.
NTRAK Modular Railroading Society, Inc.  Here you will find all manner of information about N scale modular railroading including an explanation of just what it is, how to get started in it, and how to get connected to others who are involved with it...
TTRAK, a new idea for modular N Scale modeling
SANTRAK as well as many other organizations have selected the EasyDCC products as the DCC product of choice for all digital command control functions.  To become more familiar with these products, you can go to CVP Products where you will find downloadable documentation for all their products.
Nearby Clubs
An N-Trak club located in the Austin Texas area.
The largest HO scale modeling club in San Antonio, TX.  A non-profit organization located in the Bob Clark Heritage Museum.
A.M.R.E. is a model railroading club located at the Texas Transportation Museum in San Antonio, TX.
The New Braunfels Railroad Museum is a non-profit organization dedicated to the preservation of railroad artifacts and education.
Clubs Of Interest
Northern Virginia NTRAK, Inc.  This site provides a host helpful information, pictures of modules, workshops and more

This is primarily a HO club but they have an excellent, detailed description of an NTRAK module. The construction and scenery is different and interesting.
SAN DIEGO SOCIETY OF N SCALE They have a very large N-scale layout located within the San Diego Model Railroad Museum You might want  to check out an impressive video of 99 car coal train at
Model Railroad This monthly online magazine has content for ALL scales.