Many people will have the music of their favorite artists available in some form. A DVD package of a teacher's favorite artist (not a box set, which they may well already have) should include a collection of individually selected DVDs. This will also show a degree of thought. Obscure DVDs, such as a concert recorded before an artist was really famous, would help to create a special present. The DVD could also be augmented by added extras such as music vouchers.
Buy the teacher a variety of music-related books and sheet music. Ideas for books include songbooks and biographies of famous musicians and composers. When the music teacher's interests span all genres of music, then the gift should be a mix of as much music as possible. Sheet-music gifts should be partly influenced by the songs and music learned in class but also by remembering what the teacher's favorite songs are.
A recording of performance by the music teacher's students, involving music and songs learned in class, can be put onto a CD. This will give the present a particularly personal appeal, and a teacher will be doubly pleased -- to receive the gift and to realize that the class has learned what she has taught. A humorous, affectionate song, written and performed with the teacher in mind, would make a suitable last song on the CD.
Knowledge of a teacher's favorite musical instrument can give students another idea for a music-related gift. A music teacher will normally have a number of instruments he especially likes listening to and playing. Make sure that the price is within reason and that the instrument is playable before buying it. Encourage the teacher to try out the instrument in class.