Music Quizzes, Games and Help with Music by Ms. Garrett http://www.musictechteacher.com/musicquizzes.htm

Music and sound effects with user-friendly copyright. http://www.freeplaymusic.com/
All kinds of tracks: http://www.playlist.com/
Free Internet Radio: http://www.pandora.com/
Free ART & Music Federal Resources: http://www.free.ed.gov/subjects.cfm?subject_id=1
Kids Can Rock: http://kidsrock.com/
For grade 3-5 classes - Classics for Kids site at www.classicsforkids.com It is chock full of music stuff from instruments to music careers to composers with lots of audio, downloadable worksheets, and online games. San Fransisco Symphony has a nice/fun site too at www.sfskids.org. There are nice resources at the Great Performances (PBS) for educators as well. The multimedia pages are at www.pbs.org/wnet/gperf/multimedia/multimedia.html and lesson plans at www.pbs.org/wnet/gperf/education/education.html. Opera Basics videos are available for different voice categories. The largest free choral sheetmusic sites out there is the Choral Music Public Domain Library www.cpdl.org and A huge music distributor is J.W. Pepper at www.jwpepper.com


Music association websites: MENC (The National Association of Music Educators) at www.menc.org.
PA state music association at www.pmea.net which has state information about festivals, conferences, auditions, and events. New York music association: www.nyssma.org.
American Choral Directors Association (ACDA) at acda.org. (Not as many lesson plans here, but lots of festival and event information and journal articles.)
String players/teachers - the American String Teachers Association at www.astaweb.com.
ChoralNet is a global choral community - www.choralnet.org.
Chorus America can be found at www.chorusamerica.org.
Barbershop Harmony Society at www.barbershop.org has lots of barbershop information, downloadable music, etc., and a free introduction guide.
Technology Institute for Music Educators (TI:ME) at www.ti-me.org (Lots of resources including music technology lessons and helps (for members) as well as information about professional development and TI:ME certification).
Music technology - SoundTree at www.soundtree.com where they have gear to buy as well as technology lesson plans and informative and helpful articles.

As for music advocacy sites there's www.musicforall.org, and www.schoolmusicmatters.com. Many of the association websites also have advocacy information.
There's also the American Music Conference at www.amc-music.com and www.childrensmusicworkshop.com. These sites also include a broad range of music information much like MENC above. The Children's Music Workshop even has "how to buy/rent/practice, etc....." articles, a plethora or music links, and even a music theory tutor.

++Thanks to my sister, a teacher in CT, for a lot of these sites.