Music

Billboard Online Charts - Contains the music billboard charts listing the countries top songs.
http://www.billboard.com/bbcom/charts.jsp
The MHN Instrument Encyclopedia - Contains information about musical instruments from around the world. It also has a link to a glossary of musical terms.
http://www.si.umich.edu/chico/instrument/enclpdia1.html
Ethnomusicology, folk music, and world music - This site explains different types of music from around the world. It also has a listening center so users can hear some of the selections as well.
http://www.lib.washington.edu/music/world.html
Music for Presentations - This site offers free music clips for use in powerpoint presentations that don't infringe on artists' copyright.
http://freeplaymusic.com/

Art

Archives of American Art from the Smithsonian - Contains loads of information about artists, works of art, and design.
http://www.si.edu/art_and_design/
Artslynx - This site also contains information about artwork and artists. It also contains some wonderful information about photography.
http://www.artslynx.org/vis/index.htm
Kidsweb - Contains links to famous art museums and artist pages.
http://www.npac.syr.edu/textbook/kidsweb/Arts/art.html