There's More to Playing the Piano - A thorough explanation of music theory with practical keyboard activities and video links for each topic
David Hall
The Violin in 5ths - Developing Intonation and Sound
Rodney Friend
The Art Of Piano Fingering - A New Approach to Scales and Arpeggios
Penelope Roskell
Tuning In - Practical Psychology for Musicians who are Teaching Learning and Performing
Lucinda Mackworth-Young