The Columbia Regional Geospatial Service Center (CRGSC) is a fine source for Texas GIS datasets including orthophotos, vector data products, GPS base station locations, Landsat and SPOT imagery, and more. Thanks to Justing for this fine tip! See
http://www.crgsc.org/ - See
http://www.crgsc.org/

Columbia Regional Geospatial Service Center (Texas)