Texas music isn't just about country music, though that's probably a big part of it. And Texas is home to some great music makers, the late great Stevie Ray Vaughn, Willie Nelson, George Strait, Marcia Ball, ZZ Top, Janis Joplin and even Beyonce just to name a few. One of my personal favorites is Kelly Willis, wife of Bruce Robison.
There's a certain something you'll hear from some Texas country artists, though it's not completely indigenous to Texas. It's something that reminds me a lot of Willie Nelson. Some people call it Texana; some people call it Americana. Or maybe Texana is a subgenre of Americana--see writing genre's aren't the only ones that can get a bit...tangled. *g* But what it is is an honest, raw, grass roots sound. Pat Green comes to mind, as does Jack Ingram, Sonny Burgess, Robert Earl Keen and Cory Morrow, Bruce and Charlie Robison as well-known Texas musicians who personify that sound.
Much like in writing where small press and e-publishing struggle against more moneyed competition, in a world where Nashville is king, Americana is the fighting underdog. In case you're still confused, the Americana Music Association defines Americana as: American roots music based on the traditions of country. While the musical model can be traced back to the Elvis Presley marriage of hillbilly and R&B that birthed rock n roll, Americana as a radio format developed during the 1990's as a reaction to the highly polished sound that defined the mainstream music of that decade.
Here's a few links for you:
The Americana Music Association
I'll add to this list as I expand my research.