author of a new Ranger history (The Texas Rangers: Wearing the Cinco Peso, 1821-1900 by Mike Cox. (New York: Forge Books, 496 pages, $25.95 )) comments in his own blog "Lone Star Book Blog" on a collection of other very recent other Ranger volumes.
Read his "Roundin' Up Ranger Books" for insightful comments and fuller bibliographical citations.
Some titles that Mike identifies are:
Lawmen on the Texas Frontier: Rangers and Sheriffs by Candice DuCoin.
Captain J.A. Brooks Texas Ranger by Paul N. Spellman.
Unbridled Cowboy: Joseph B. Fussell, edited by E.R. Fussell.
Captain Ransom, Texas Ranger: An American Hero, 1874-1918 by Pat Goodrich.
Law on the Last Frontier: Texas Ranger Arthur Hill by S.E. Spinks.
One Ranger Returns by Joaquin Jackson with James L. Haley.
Lone Star Lawmen: The Second Century of the Texas Rangers by Robert Utley.