http://teachertube.com/--This site is similar to YouTube.com, except that teachers are the ones maintaining it. Inappropriate videos are flagged, all videos are rated and tagged so that they are easily searchable for content and efficacy. Yes!
http://www.musictheory.net/--For Music Educators, this website is a great place to offer enrichment for students that goes beyond the rote learning and performing of music. This site is great for teaching music theory basics.
http://www.practicesightreading.com/--One of the marks of a great musician is the ability to see music printed on a page and be able to audiate (hear it) in his/her head. This skill is one that can be honed over time, but like most languages, music is best learned with lots of practice reading at younger ages. This site offers a "deluxe" version of itself, but is effective in its "free" form.
http://www.nafme.org/--Finally, the National Association for Music Education's website provides music educators with support, standards, and supplies. In programs that are frequently considered "extra" in many educational circles, it is important to remember that state and national standards have been set and must be adhered to.