This SanFransisco Symphony website is tons of fun for kids (and adults too...).  Students can learn about, look at, and hear the different instruments in the orchestra, and play around with the staff, tempo, rhythm, pitch, harmony, symbols, instrumentation, and composition.

 

This is an awesome site - you can search for instruments geographically by clicking on a map, or categorically by clicking on an instrument group (strings, percussion, etc.).  This site includes pictures, history and sounds of instruments.

 

This is an extensive directory of children's sites on the web - it is broken up into categories including Biography/History, Geography, Language Arts, Math, Music, Science/Nature & Fun.

 

This site offers information on the 6 eras in music, composers, and glossary of music terms.

 

Made by students for students, this site is a part of the ThinkQuest organization which encourages students to make educational websites under the guidance of teachers or other adults.  Musically Inclined has a library, including history of music and how music works.  It also has a virtual concert, interactive games, and discussions.

 

Good site if you are one of those people who like to write musical tidbits on your board...