Horn
Technique
Some Random Ideas and Reminders for Improving Accuracy by Nicholas Smith
Video - Rex Richardson Basic Flexibility for Brass Players - Rex is trumpet player, but the flexibility exercises he demonstrates are good for all brasses.
Horn Techniques - shoft Wikipedia article; see also this one with brief links to sections on posture, right hand, fingering chart, breathing, embouchure, articulation, tips & tricks, and transposition.
Horn Technique - covers a variety of topics, part of "Horn Player's 'Where to Find'"
The Standley Routine - description of Forrest Standley's system of scales and arpeggios.
Vibrato - by Thomas Bacon
Power Scales - by Jeffrey Agrell (pdf download)