rockhall.com/hof – You can find a lot of rock history on the Rock and Roll Hall of Fame website.
history-of-rock.com – A good resource for early rock n’ roll history.
allmusic.com – The All Music Guide’s on-line Allmusiczine has in-depth interviews, reviews and news. Check out the Music Maps and Music Styles section for some interesting history.
jahsonic.com/music.html – An encyclopedic, personal (Jan Geerinck) and very interesting history of just about every style you can think of as Popular Music: Blues, Soul, Disco, House, Reggae, Jazz, Funk, Jazz-Funk, Dub, Rap and Hip-Hop, Garage, Techno, Electro, Rare Groove, Acid Jazz, AfroBeat, Rock, Brazil, and R&B.
rockabillyhall.com – Visit the Rockabilly Hall of Fame for the latest news and to read artist bios, reviews and articles.
blueslyrics.tripod.com/blueshistory.htm – An excellent starting place to explore blues history.
A couple good sites for jazz history: