For jazz improv, there are approximately seventy-seven gazillion books, articles, playalongs, and everything else out there. Visit Jamey Aebersold’s web site and start ordering – you’ll never get to the end of the offerings.
For classical improv and creative music in general, some of the jazz stuff is useful, but is usually not the best place to start. The list of useful and appropriate materials is much smaller.
If you are a band, choir, or orchestra director interested in trying some non jazz improvisation, the list is smaller yet. I just applied to the Midwest Band Clinic (Dec. 19-22) to give a presentation on improv for large ensembles; as part of a handout for this proposed (we’ll have to wait and see if it is eventually accepted) talk, I made a list of some resources for the band director and I’d like to share that with you now (it’s possible that it will be updated and/or extended by the time Midwest rolls around, should this proposal be accepted).
Agrell, Jeffrey, Improvisation Games for Classical Musicians
Agrell, Jeffrey, Improvisation Games for One Player
Blog: Improv Insights (http://improvinsights.com) by Jeffrey Agrell and Evan Mazunik
Feldman, Evan, and Contzius, Ari, Instrumental Music Education: Teaching with the Musical and Practical in Harmony
Christopher Azzara, Richard Grunow, Edwin Gordon, Creativity in Improvisation Vol. 1 & 2 [with CD]
Herb, Thomas, Teaching Improvisation.. in Concert Band?!?: Improvisation Activities Incorporating Concert Band Repertoire
Julie Lyonn Lieberman, The Creative Band and Orchestra Director
Edward S. Lisk, Intangibles of Musical Performance
Walter Thompson – Soundpainting: The Art of Live Composition. Manual [with DVD; see www.soundpainting.com; also videos in YouTube]
Keith Hill, “Improvise Intentionally “ Available online at: www.musicalratio.com/gpage1.html13.html
Keith Hill, “Improvise Intentionally Part 2” Available at: www.musicalratio.com/gpage1.html14.html
Charles Young, “Is Music a Dead Language?” Available at: www.uwsp.edu/music/people/faculty/cyoung/resources/deadlanguage.htm
David Rosenboom, “Improvisation and Composition – Synthesis and Integration into the Music Curriculum” Available as a pdf file online at http://music.calarts.edu/~david/writings/articles_docs/NASM.improv.composite.pdf
Bill Dobbins, “Improvisation: An Essential Element of Musical Proficiency,” Music Educators Journal, January 1980, p. 36-41.
Harold M. Best, “Music Curricula in the Future” Available at www.leaderu.com/offices/haroldbest/curricula.html
They’re all good; I think if I had to pick the most useful of these for a band director, I would probably advise my (big) book, J.L Lieberman’s The Creative Band and Orchestra Director, and Edward Lisk’s Intangibles of Musical Performance as the best places to start.
Oh, and of course, the mother of all improv books, Stephen Nachmanovitch’s Free Play, a book that every carbon-based life form should read and re-read (even if you never improvise musically).