All Music Guide - Portal built around articles by music journalists describing music genres, with links and reviews.
Audiogalaxy: Glossary of Musical Styles - Hundreds of sub-genres defined in non-technical language mentioning sample artists. Organized under headings such as pop, hip-hop, jazz, blues, classical, Latin, modern rock, rock, and heavy metal.
Christian Music Place: Artists by Genre - About two dozen musical genres including blues, a capella, dance/techno, and Southern gospel, with as many as several hundred links to Christian music artists in each.
DataDragon: Music Genre Sampler - Children's site with simple definitions of a few genres including rock, Celtic, and classical with artist and site links.
Ectophiles Guide by Genre - Self-described "Guide to Good Music" from a group founded in 1991 to support the music of singer Happy Rhodes. Links to artists, almost entirely female vocalists, sorted by genre such as pop, blues, experimental, performance art, beautiful and fierce, and traditional.
Indiana University School of Music: Genres - Categorized links organized by researchers at the William and Gayle Cook Music Library. Categories include 20th-Century music, ancient music, band music, tango, flamenco, ragtime, and choral music.
Music Web Hunter: Styles & Genres - Ken Davies has grouped resources in five categories: classical, folk/ethnic/world, jazz, musicals/operas/theater, and pop/rock/country.
Representing Musical Genre: A State of the Art - Journal of New Music Research article from 2003 discusses manual, prescriptive, and emergent approaches to genre classification for the European CUIDADO project, Content-Based Unified Interfaces and Descriptors for Audio/Music Databases Available Online. [PDF]
A Taxonomy of Musical Genres - Two French experts re-define genres to improve musical databases for electronic distribution, paper submitted to a conference in Paris in 2000. [PDF]
Wikipedia: Musical Genre - Brief explanation of the way styles can be defined by region, chronology, technical requirements, marketing trends, or the ideas of critics. Extensively linked to sub-genres and examples of significant artists.