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).