The best place to start is the Naxos Music Library.
You can search by:
Google Video can be a valuable source for videos of traditional music.
To search, try [countryname] music
If you get lots of pop music, try adding traditional.
Garland Encyclopedia of World Music
To listen to audio content, use the links on the left.
To read text, click on the image of the volume you'd like to view, e.g. Middle East