Arab music reference materials
The Garland Encyclopedia of World Music online (see especially Volume 6). Also see the offline versions; not everything was included online.
Grove Music Online (not currently available off-campus)
Wikipedia articles on Arab music
Maqamworld: Theory and instruments (superb site!)
Contemporary World Music (full audio database)
Smithsonian Global Sound (full audio database)
Smithsonian Folkways recordings (with 30 second clips and liner notes)