Books by Louis L'Amour or Zane Grey, really are great. One of my favorite authors is Cameron Judd, he happens to live near me but was my favorite author before I found that out and got to meet him. He has a great trilogy called the Tennessee Frontier Trilogy, the Overmountain Men, The Border Men, and the Canebrake Men. If you are a hardcore western fan he has those too, Corrigan, Snow Sky, and Mr. Little John just to name a few.
http://www.amazon.com/s/ref=nb_ss_gw?url=search-alias%3Dstripbooks&field-keywords=cameron+judd&x=0&y=0
There is a new book out called Many A River, by Elmer Kelton that I really enjoyed
http://www.amazon.com/s/ref=nb_ss_b?url=search-alias%3Dstripbooks&field-keywords=elmer+kelton&x=0&y=0
Country singer, Willie Nelson just released a western called A Tale Out Of Luck thats pretty good
http://www.amazon.com/Tale-Out-Luck-Novel/dp/1599957329/ref=sr_1_2?ie=UTF8&s=books&qid=1228782131&sr=1-2