Women make up half of the population, but most of the music we study and listen to was written by men. Why is that?
Women are great composers, too. Why aren't they being heard?
Women composers by time period -- it may surprise you how many of these women you have never heard of--
Women composers of ragtime -- includes an A-Z list with links to about half the actual music (most ragtime music is in the public domain)
Women composers of classical music whose works have been recorded by a commercial label
Orchestral music by women of African descent
Dr. Christopher Reynolds (UC Davis) collected 3000 songs composed by women. See the finding aid for this collection.
Choral Public Domain (CPDL) list of women composers with links to their music.
IMSLP's list of women composers with links to their music
Call number for books about women and music: ML 82 -- call number browse (use the NEXT button to keep scrolling through)
Representative sample of books/media on the topic:
Women, music and leadership by
Women, Music and Leadership offers a wide-ranging survey of women in musical leadership and their experiences, highlighting women's achievements and considering how they negotiate the challenges of the leadership space in music.
The Routledge Handbook of Women's Work in Music by
The Routledge Handbook of Women's Work in Music presents a unique collection of core research by academics and music practitioners from around the world, engaging with an extraordinarily wide range of topics on women's contributions to Western and Eastern art music, popular music, world music, music education, ethnomusicology as well as in the music industries. The handbook falls into six parts. Part I serves as an introduction to the rich variety of subject matter the reader can expect to encounter in the handbook as a whole. Part II focuses on what might be termed the more traditional strand of feminist musicology - research which highlights the work of historical and/or neglected composers. Part III explores topics concerned with feminist aesthetics and music creation and Part IV focuses on questions addressing the performance and reception of music and musicians. The narrative of the handbook shifts in Part V to focus on opportunities and leadership in the music professions from a Western perspective. The final section of the handbook (Part VI) provides new frames of context for women's positions as workers, educators, patrons, activists and promoters of music. This is a key reference work for advanced undergraduates, postgraduates and researchers in music and gender.
Uncovering Music of Early European Women (1250-1750) by 
Women in Music by
Women in Music: A Research and Information Guide is an annotated bibliography emerging from more than twenty-five years of feminist scholarship on music. This book testifies to the great variety of subjects and approaches represented in over two decades of published writings on women, their work, and the important roles that feminist outlooks have played in formerly male-oriented academic scholarship or journalistic musings on women and music.
From Convent to Concert Hall by 
Yours for a song: the women of Tin Pan Alley