The Handbook of Texas Online, part of the Texas State Historical Association, is a super resource for western writers. It has a searchable database and is print-friendly. A bibliography is included at the end of every article.
I just finished printing out articles on every ranch listed in the book Historic Ranches of Texas in order to cross-check information as well as be able to highlight important facts--something I don't want to do in the book itself.
And speaking of the book itself--when I am finished with my research, I intend to carefully take the book apart and remove the superb paintings of J.U. Salvant and frame them. When I get moved home, I'm going to have walls and walls of western "stuff" in my study!