Musopen is an online library classical music of music recordings and sheet music that are in the public domain. All of the recordings on Musopen can be downloaded and or be embedded into your blog or website. The sheet music offered by Musopen is hosted by Scribd from where you can download or print the sheet music.
Applications for Education
Musopen could be a good resource for teachers of music theory as well as teachers of music performance. You could also use Musopen as an example of uses of public domain works.
Here are some related items that may be of interest to you:
Arts Edge - Podcasts and Lesson Plans
Classics for Kids - Classical Music Lesson Plans
Music Theory Lessons and Tutorials