Classical Music
Boston Phoenix's Classical Listings
http://www.newenglandconservatory.edu/calendar/
Longy School of Music
BSO: for Tanglewood 2001 Events (display interface is simply dismal)
Jazz
Berklee Calendar
Folk
Club Passim
Kendall Cafe
Musi-Cal | Musi-Cal Boston listings
Rock
nexticketing hikes prices up $5.50 per ticket for handling charges
but lists dates for: Avalon
Paradise
Axis Bill's
Bar
Boston Phoenix Clubs by Night
Johnny D's Calendar
this month at Lilli's
Matador Records Tour Dates
Middle East Schedule
Thrill Jockey Records Tour Dates
TicketMaster seems to have schedules well ahead of the Phoenix (if you know what you're looking for).
BAM! - Boston Area Music (very outdated)
OOOOLLLD (1997!) Boston Music Scene
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keep an eye out: Knitting Factory, NYC
Maxwell's, Hoboken
Art & Museums
Arts Around Boston - Guide to Art Galleries
Book Tours
Wordsworth Author Events
Harvard Book Store Events
Brookline Booksmith Events
Boston.com listings