History of Electronic Music
http://www.google.com/search?hl=en&lr=&safe=off&q=%22music+since+1945%22
History of Electronic music contains a four-part introduction to the history and development of the genre. Additionally, a timeline and student written essays on key artists are also included.
Chance Music
http://www.scu.edu.au/schools/edu/student_pages/2000/ajohnson/chance.htm
A brief description of the indeterminacy or "chance" music approaches of artists like John Cage is provided at this site. Site also includes a composition task exercise related to the approach.
Minimalism
http://www.scu.edu.au/schools/edu/student_pages/2000/ajohnson/minim.htm
A brief description on the minimalist approach in works by artists like Steve Reich and and Phillip Glass is presented at this site. Site also includes a composition task exercise related to the approach.