The Literature section of the Forum of the web site of the International Horn Society also includes questions and comments about horn etudes.
60 Etudes for Low Horn, Op. 6 by G. Kopprasch - Free sheet music pdf files of the famous etude collection from IMSLP.
The Original Kopprasch Etudes - article by - guess who: John Ericson. See also his "Later Editions of Kopprasch Etudes" and his “Download the Original Kopprasch Etudes”
Kopprasch Studies - discussion on Hornplayer.net
Index to Horn Etudes - article by Jeffrey Agrell, categorizing specific etudes according to technique
The Personal Etude - article by Jeffrey Agrell on how and why to compose your own etudes
Twenty Difficult Etudes for the Horn's Middle Register -by Daniel Grabois of the Meridian Arts Ensemble
40 Characteristic Etudes for Horn by H. Kling - short teaser samples of Stephen Hager performing them. Order the CD to hear them all!