For loads of other public domain scores/recordings, see the Petrucci music library at http://www.imslp.org. As a music academic/teacher, IMSLP is invaluable for me. There are also CC-licensed recordings, though I don't use them much myself.
Much of what they have there are 19th-century editions, which are now of course in the public domain. You might think that 150+ year-old editions aren't super-valuable, but many of them are from the Breitkopf & Härtel collected works editions. These editions are some of the most important works of 19th-century music scholarship, and were collected, edited, and subscribed to by important figures. Robert Schumann's works, for example, were all edited by Clara Schumann (an important composer in her own right), and Johannes Brahms is listed among the subscribers to the Bach complete works edition (among many others).
IMSLP is great, and these new releases will be hosted there too. In fact, you can find the 2012 Open Goldberg Variations (similar to this project) on IMSLP.
What IMSLP doesn't have a lot of is new, studio recordings, with the highest standard of playing and recording engineering. That's what the Open Well-Tempered Clavier provides!
CC-licensed recordings of 'standard repertoire' chamber music (no scores) by a variety of performers, some famous and some students at the Isabella Gardner Museum Web site. One of the nicest podcasts. Around 10Gb of 128/192 kb/s mp3s
Much of what they have there are 19th-century editions, which are now of course in the public domain. You might think that 150+ year-old editions aren't super-valuable, but many of them are from the Breitkopf & Härtel collected works editions. These editions are some of the most important works of 19th-century music scholarship, and were collected, edited, and subscribed to by important figures. Robert Schumann's works, for example, were all edited by Clara Schumann (an important composer in her own right), and Johannes Brahms is listed among the subscribers to the Bach complete works edition (among many others).