A Passion for Jazz has a great breakdown of the styles of jazz, from its beginnings in the 19th century to contemporary jazz styles from the 1980s and 1990s. Each style is covered in a couple of paragraphs which describe the music and its place in the jazz timeline. A commendably comprehensive list, the only thing I would want to add to it would be the jazz-world fusion artists such as Rudresh Mahanthappa, John McLaughlin, Gabriel Alegria, and many others. Regardless, A Passion for Jazz has provided a fantastic resource for students and fans of jazz.
Check it out here: Styles of Jazz Music Article